Merge pull request #12 from nden/pep8-pylint

Pep8 pylint

35 files changed, 1474 insertions, 1427 deletions

diff --git a/stwcs/distortion/coeff_converter.py b/stwcs/distortion/coeff_converter.py
index 415b512..99cf74d 100644
--- a/stwcs/distortion/coeff_converter.py
+++ b/stwcs/distortion/coeff_converter.py
@@ -1,9 +1,10 @@
-from __future__ import division, print_function # confidence high
+from __future__ import (absolute_import, unicode_literals, division, print_function)
 
 import numpy as np
 from astropy.io import fits
 from astropy import wcs as pywcs
 
+
 def sip2idc(wcs):
     """
     Converts SIP style coefficients to IDCTAB coefficients.
@@ -49,28 +50,28 @@ def sip2idc(wcs):
         print('Input to sip2idc must be a PyFITS header or a wcsutil.HSTWCS object\n')
         return
 
-
     if None in [ocx10, ocx11, ocy10, ocy11]:
         print('First order IDC coefficients not found, exiting ...\n')
         return None, None
     idc_coeff = np.array([[ocx11, ocx10], [ocy11, ocy10]])
-    cx = np.zeros((order+1,order+1), dtype=np.double)
-    cy = np.zeros((order+1,order+1), dtype=np.double)
-    for n in range(order+1):
-        for m in range(order+1):
-            if n >= m and n>=2:
-                sipval = np.array([[sipa[m,n-m]],[sipb[m,n-m]]])
+    cx = np.zeros((order + 1, order + 1), dtype=np.double)
+    cy = np.zeros((order + 1, order + 1), dtype=np.double)
+    for n in range(order + 1):
+        for m in range(order + 1):
+            if n >= m and n >= 2:
+                sipval = np.array([[sipa[m, n - m]], [sipb[m, n - m]]])
                 idcval = np.dot(idc_coeff, sipval)
-                cx[n,m] = idcval[0]
-                cy[n,m] = idcval[1]
+                cx[n, m] = idcval[0]
+                cy[n, m] = idcval[1]
 
-    cx[1,0] = ocx10
-    cx[1,1] = ocx11
-    cy[1,0] = ocy10
-    cy[1,1] = ocy11
+    cx[1, 0] = ocx10
+    cx[1, 1] = ocx11
+    cy[1, 0] = ocy10
+    cy[1, 1] = ocy11
 
     return cx, cy
 
+
 def _read_sip_kw(header):
     """
     Reads SIP header keywords and returns an array of coefficients.
@@ -84,15 +85,15 @@ def _read_sip_kw(header):
                 "keyword for SIP distortion")
 
         m = int(header["A_ORDER"])
-        a = np.zeros((m+1, m+1), np.double)
-        for i in range(m+1):
-            for j in range(m-i+1):
+        a = np.zeros((m + 1, m + 1), np.double)
+        for i in range(m + 1):
+            for j in range(m - i + 1):
                 a[i, j] = header.get("A_%d_%d" % (i, j), 0.0)
 
         m = int(header["B_ORDER"])
-        b = np.zeros((m+1, m+1), np.double)
-        for i in range(m+1):
-            for j in range(m-i+1):
+        b = np.zeros((m + 1, m + 1), np.double)
+        for i in range(m + 1):
+            for j in range(m - i + 1):
                 b[i, j] = header.get("B_%d_%d" % (i, j), 0.0)
     elif "B_ORDER" in header:
         raise ValueError(
@@ -102,7 +103,7 @@ def _read_sip_kw(header):
         a = None
         b = None
 
-    return a , b
+    return a, b
 
 
 """
diff --git a/stwcs/distortion/models.py b/stwcs/distortion/models.py
index 231a9f1..136c6cf 100644
--- a/stwcs/distortion/models.py
+++ b/stwcs/distortion/models.py
@@ -1,14 +1,9 @@
-from __future__ import absolute_import, division, print_function # confidence high
-
+from __future__ import absolute_import, division, print_function
 
 import numpy as np
-
-# Import PyDrizzle utility modules
 from . import mutil
 from .mutil import combin
 
-yes = True
-no = False
 
 #################
 #
@@ -72,8 +67,8 @@ class GeometryModel:
         to the reference position of the chip.
         """
 
-        _cxs = np.zeros(shape=self.cx.shape,dtype=self.cx.dtype)
-        _cys = np.zeros(shape=self.cy.shape,dtype=self.cy.dtype)
+        _cxs = np.zeros(shape=self.cx.shape, dtype=self.cx.dtype)
+        _cys = np.zeros(shape=self.cy.shape, dtype=self.cy.dtype)
         _k = self.norder + 1
         # loop over each input coefficient
         for m in range(_k):
@@ -83,15 +78,17 @@ class GeometryModel:
                     _ilist = list(range(m, _k))
                     # sum from m to k
                     for i in _ilist:
-                        _jlist = list(range(n, i - (m-n)+1))
+                        _jlist = list(range(n, i - (m - n) + 1))
                         # sum from n to i-(m-n)
                         for j in _jlist:
-                            _cxs[m,n] += self.cx[i,j]*combin(j,n)*combin((i-j),(m-n))*pow(xs,(j-n))*pow(ys,((i-j)-(m-n)))
-                            _cys[m,n] += self.cy[i,j]*combin(j,n)*combin((i-j),(m-n))*pow(xs,(j-n))*pow(ys,((i-j)-(m-n)))
+                            _cxs[m, n] += self.cx[i, j] * combin(j, n) * combin((i - j), (m - n)) * \
+                                pow(xs, (j - n)) * pow(ys, ((i - j) - (m - n)))
+                            _cys[m, n] += self.cy[i, j] * combin(j, n) * combin((i - j), (m - n)) * \
+                                pow(xs, (j - n)) * pow(ys, ((i - j) - (m - n)))
         self.cx = _cxs.copy()
         self.cy = _cys.copy()
 
-    def convert(self, tmpname, xref=None,yref=None,delta=yes):
+    def convert(self, tmpname, xref=None, yref=None, delta=True):
         """
          Open up an ASCII file, output coefficients in drizzle
           format after converting them as necessary.
@@ -104,89 +101,62 @@ class GeometryModel:
             Added ability to shift coefficients to new center for support
                 of subarrays.
         """
-        cx = self.cx/self.pscale
-        cy = self.cy/self.pscale
-        x0 = self.refpix['XDELTA'] + cx[0,0]
-        y0 = self.refpix['YDELTA'] + cy[0,0]
-        #xr = self.refpix['XREF']
-        #yr = self.refpix['YREF']
+        cx = self.cx / self.pscale
+        cy = self.cy / self.pscale
+        x0 = self.refpix['XDELTA'] + cx[0, 0]
+        y0 = self.refpix['YDELTA'] + cy[0, 0]
         xr = self.refpix['CHIP_XREF']
         yr = self.refpix['CHIP_YREF']
 
-
-
-        '''
-        if xref != None:
-            # Shift coefficients for use with drizzle
-            _xs = xref - self.refpix['XREF'] + 1.0
-            _ys = yref - self.refpix['YREF'] + 1.0
-
-
-            if _xs != 0 or _ys != 0:
-                cxs,cys= self.shift(cx, cy, _xs, _ys)
-                cx = cxs
-                cy = cys
-
-                # We only want to apply this shift to coeffs
-                # for subarray images.
-                if delta == no:
-                    cxs[0,0] = cxs[0,0] - _xs
-                    cys[0,0] = cys[0,0] - _ys
-
-                # Now, apply only the difference introduced by the distortion..
-                # i.e., (undistorted - original) shift.
-                x0 += cxs[0,0]
-                y0 += cys[0,0]
-        '''
-        self.x0 = x0 #+ 1.0
-        self.y0 = y0 #+ 1.0
+        self.x0 = x0
+        self.y0 = y0
 
         # Now, write out the coefficients into an ASCII
         # file in 'drizzle' format.
         lines = []
-
-
         lines.append('# Polynomial distortion coefficients\n')
-        lines.append('# Extracted from "%s" \n'%self.name)
-        lines.append('refpix %f %f \n'%(xr,yr))
-        if self.norder==3:
+        lines.append('# Extracted from "%s" \n' % self.name)
+        lines.append('refpix %f %f \n' % (xr, yr))
+        if self.norder == 3:
             lines.append('cubic\n')
-        elif self.norder==4:
+        elif self.norder == 4:
             lines.append('quartic\n')
-        elif self.norder==5:
+        elif self.norder == 5:
             lines.append('quintic\n')
         else:
             raise ValueError("Drizzle cannot handle poly distortions of order %d" % self.norder)
 
-        str = '%16.8f %16.8g %16.8g %16.8g %16.8g \n'% (x0,cx[1,1],cx[1,0],cx[2,2],cx[2,1])
+        str = '%16.8f %16.8g %16.8g %16.8g %16.8g \n' % (x0, cx[1, 1], cx[1, 0], cx[2, 2], cx[2, 1])
         lines.append(str)
-        str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cx[2,0],cx[3,3],cx[3,2],cx[3,1],cx[3,0])
+        str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cx[2, 0], cx[3, 3], cx[3, 2], cx[3, 1], cx[3, 0])
         lines.append(str)
-        if self.norder>3:
-            str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cx[4,4],cx[4,3],cx[4,2],cx[4,1],cx[4,0])
+        if self.norder > 3:
+            str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cx[4, 4], cx[4, 3], cx[4, 2], cx[4, 1], cx[4, 0])
             lines.append(str)
-        if self.norder>4:
-            str = '%16.8g %16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cx[5,5],cx[5,4],cx[5,3],cx[5,2],cx[5,1],cx[5,0])
+        if self.norder > 4:
+            str = '%16.8g %16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cx[5, 5], cx[5, 4], cx[5, 3], cx[5, 2], cx[5, 1], cx[5, 0])
             lines.append(str)
         lines.append("\n")
 
-        str = '%16.8f %16.8g %16.8g %16.8g %16.8g \n'% (y0,cy[1,1],cy[1,0],cy[2,2],cy[2,1])
+        str = '%16.8f %16.8g %16.8g %16.8g %16.8g \n' % (y0, cy[1, 1], cy[1, 0], cy[2, 2], cy[2, 1])
         lines.append(str)
-        str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cy[2,0],cy[3,3],cy[3,2],cy[3,1],cy[3,0])
+        str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cy[2, 0], cy[3, 3], cy[3, 2], cy[3, 1],
+                                                         cy[3, 0])
         lines.append(str)
-        if self.norder>3:
-            str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cy[4,4],cy[4,3],cy[4,2],cy[4,1],cy[4,0])
+        if self.norder > 3:
+            str = '%16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cy[4, 4], cy[4, 3], cy[4, 2],
+                                                             cy[4, 1], cy[4, 0])
             lines.append(str)
-        if self.norder>4:
-            str = '%16.8g %16.8g %16.8g %16.8g %16.8g %16.8g \n'% (cy[5,5],cy[5,4],cy[5,3],cy[5,2],cy[5,1],cy[5,0])
+        if self.norder > 4:
+            str = '%16.8g %16.8g %16.8g %16.8g %16.8g %16.8g \n' % (cy[5, 5], cy[5, 4], cy[5, 3],
+                                                                    cy[5, 2], cy[5, 1], cy[5, 0])
             lines.append(str)
 
-        output = open(tmpname,'w')
+        output = open(tmpname, 'w')
         output.writelines(lines)
         output.close()
 
-
-    def apply(self, pixpos,scale=1.0,order=None):
+    def apply(self, pixpos, scale=1.0, order=None):
         """
          Apply coefficients to a pixel position or a list of positions.
           This should be the same for all coefficients tables.
@@ -195,13 +165,13 @@ class GeometryModel:
 
         Compute delta from reference position
         """
-        
+
         """
         scale actually is a ratio of pscale/self.model.pscale
         what is pscale?
         """
-        if self.cx == None:
-            return pixpos[:,0],pixpos[:,1]
+        if self.cx is None:
+            return pixpos[:, 0], pixpos[:, 1]
 
         if order is None:
             order = self.norder
@@ -209,29 +179,29 @@ class GeometryModel:
         # Apply in the same way that 'drizzle' would...
         _cx = self.cx / (self.pscale * scale)
         _cy = self.cy / (self.pscale * scale)
-        _convert = no
+        _convert = False
         _p = pixpos
 
         # Do NOT include any zero-point terms in CX,CY here
         # as they should not be scaled by plate-scale like rest
         # of coeffs...  This makes the computations consistent
         # with 'drizzle'.  WJH 17-Feb-2004
-        _cx[0,0] = 0.
-        _cy[0,0] = 0.
+        _cx[0, 0] = 0.
+        _cy[0, 0] = 0.
 
         if isinstance(_p, list) or isinstance(_p, tuple):
-            _p = np.array(_p,dtype=np.float64)
-            _convert = yes
+            _p = np.array(_p, dtype=np.float64)
+            _convert = True
 
-        dxy = _p - (self.refpix['XREF'],self.refpix['YREF'])
+        dxy = _p - (self.refpix['XREF'], self.refpix['YREF'])
         # Apply coefficients from distortion model here...
         c = _p * 0.
-        for i in range(order+1):
-            for j in range(i+1):
-                c[:,0] = c[:,0] + _cx[i][j] * pow(dxy[:,0],j) * pow(dxy[:,1],(i-j))
-                c[:,1] = c[:,1] + _cy[i][j] * pow(dxy[:,0],j) * pow(dxy[:,1],(i-j))
-        xc = c[:,0]
-        yc = c[:,1]
+        for i in range(order + 1):
+            for j in range(i + 1):
+                c[:, 0] = c[:, 0] + _cx[i][j] * pow(dxy[:, 0], j) * pow(dxy[:, 1], (i - j))
+                c[:, 1] = c[:, 1] + _cy[i][j] * pow(dxy[:, 0], j) * pow(dxy[:, 1], (i - j))
+        xc = c[:, 0]
+        yc = c[:, 1]
 
         # Convert results back to same form as original input
         if _convert:
@@ -242,11 +212,11 @@ class GeometryModel:
                 xc = xc[0]
                 yc = yc[0]
 
-        return xc,yc
+        return xc, yc
 
-    def setPScaleCoeffs(self,pscale):
-        self.cx[1,1] = pscale
-        self.cy[1,0] = pscale
+    def setPScaleCoeffs(self, pscale):
+        self.cx[1, 1] = pscale
+        self.cy[1, 0] = pscale
 
         self.refpix['PSCALE'] = pscale
         self.pscale = pscale
@@ -259,7 +229,7 @@ class IDCModel(GeometryModel):
     We also need to read in SCALE, XCOM,YCOM, XREF,YREF as well.
     """
     def __init__(self, idcfile, date=None, chip=1, direction='forward',
-                filter1='CLEAR1',filter2='CLEAR2',offtab=None,  binned=1):
+                 filter1='CLEAR1', filter2='CLEAR2', offtab=None, binned=1):
         GeometryModel.__init__(self)
         #
         # Norder must be derived from the coeffs file itself,
@@ -269,9 +239,9 @@ class IDCModel(GeometryModel):
         # Populate cx,cy,scale, and other variables here.
         #
         self.name = idcfile
-        self.cx,self.cy,self.refpix,self.norder = mutil.readIDCtab(idcfile,
-                        chip=chip,direction=direction,filter1=filter1,filter2=filter2,
-                date=date, offtab=offtab)
+        self.cx, self.cy, self.refpix, self.norder = mutil.readIDCtab(idcfile,
+                                                                      chip=chip, direction=direction, filter1=filter1, filter2=filter2,
+                                                                      date=date, offtab=offtab)
 
         if 'empty_model' in self.refpix and self.refpix['empty_model']:
             pass
@@ -285,61 +255,54 @@ class IDCModel(GeometryModel):
             self.refpix['YSIZE'] = self.refpix['YSIZE'] / binned
 
         self.pscale = self.refpix['PSCALE']
-        
+
 
 class WCSModel(GeometryModel):
     """
     This class sets up a distortion model based on coefficients
     found in the image header.
     """
-    def __init__(self,header,rootname):
+    def __init__(self, header, rootname):
         GeometryModel.__init__(self)
 
-
         if 'rootname' in header:
             self.name = header['rootname']
         else:
             self.name = rootname
         # Initialize all necessary distortion arrays with
         # default model...
-        #self.cx,self.cy,self.refpix,self.order = mutil.defaultModel()
+        # self.cx,self.cy,self.refpix,self.order = mutil.defaultModel()
 
         # Read in values from header, and update distortion arrays.
-        self.cx,self.cy,self.refpix,self.norder = mutil.readWCSCoeffs(header)
+        self.cx, self.cy, self.refpix, self.norder = mutil.readWCSCoeffs(header)
 
         self.pscale = self.refpix['PSCALE']
 
 
-
 class DrizzleModel(GeometryModel):
     """
     This class will read in an ASCII Cubic
     drizzle coeffs file and populate the cx,cy arrays.
     """
 
-    def __init__(self, idcfile, scale = None):
+    def __init__(self, idcfile, scale=None):
         GeometryModel.__init__(self)
         #
         # We now need to read in the file, populate cx,cy, and
         # other variables as necessary.
         #
         self.name = idcfile
-        self.cx,self.cy,self.refpix,self.norder = mutil.readCubicTable(idcfile)
+        self.cx, self.cy, self.refpix, self.norder = mutil.readCubicTable(idcfile)
 
-        # scale is the ratio wcs.pscale/model.pscale. 
+        # scale is the ratio wcs.pscale/model.pscale.
         # model.pscale for WFPC2 is passed from REFDATA.
         # This is needed for WFPC2 binned data.
-        
-        if scale != None:
+
+        if scale is not None:
             self.pscale = scale
         else:
             self.pscale = self.refpix['PSCALE']
 
-        """
-        The above definition looks wrong.
-        In one case it's a ratio in the other it's pscale.
-        
-        """
 
 class TraugerModel(GeometryModel):
     """
@@ -349,14 +312,8 @@ class TraugerModel(GeometryModel):
     """
     NORDER = 3
 
-    def __init__(self, idcfile,lam):
+    def __init__(self, idcfile, lam):
         GeometryModel.__init__(self)
         self.name = idcfile
-        self.cx,self.cy,self.refpix,self.norder = mutil.readTraugerTable(idcfile,lam)
+        self.cx, self.cy, self.refpix, self.norder = mutil.readTraugerTable(idcfile, lam)
         self.pscale = self.refpix['PSCALE']
-        #
-        # Read in file here.
-        # Populate cx,cy, and other variables.
-        #
-
-
diff --git a/stwcs/distortion/mutil.py b/stwcs/distortion/mutil.py
index ed6a1ea..0e193c8 100644
--- a/stwcs/distortion/mutil.py
+++ b/stwcs/distortion/mutil.py
@@ -1,25 +1,22 @@
-from __future__ import division, print_function # confidence high
+from __future__ import division, print_function
 
 from stsci.tools import fileutil
 import numpy as np
 import calendar
 
-# Set up IRAF-compatible Boolean values
-yes = True
-no = False
-
 # This function read the IDC table and generates the two matrices with
 # the geometric correction coefficients.
 #
 #       INPUT: FITS object of open IDC table
 #       OUTPUT: coefficient matrices for Fx and Fy
 #
-#### If 'tabname' == None: This should return a default, undistorted
-####                        solution.
+#    If 'tabname' == None: This should return a default, undistorted
+#                            solution.
 #
 
-def readIDCtab (tabname, chip=1, date=None, direction='forward',
-                filter1=None,filter2=None, offtab=None):
+
+def readIDCtab(tabname, chip=1, date=None, direction='forward',
+               filter1=None, filter2=None, offtab=None):
 
     """
         Read IDCTAB, and optional OFFTAB if sepcified, and generate
@@ -30,17 +27,17 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
 
     """
 
- # Return a default geometry model if no IDCTAB filename
+    # Return a default geometry model if no IDCTAB filename
     # is given.  This model will not distort the data in any way.
-    if tabname == None:
+    if tabname is None:
         print('Warning: No IDCTAB specified! No distortion correction will be applied.')
         return defaultModel()
 
     # Implement default values for filters here to avoid the default
     # being overwritten by values of None passed by user.
-    if filter1 == None or filter1.find('CLEAR') == 0 or filter1.strip() == '':
+    if filter1 is None or filter1.find('CLEAR') == 0 or filter1.strip() == '':
         filter1 = 'CLEAR'
-    if filter2 == None or filter2.find('CLEAR') == 0 or filter2.strip() == '':
+    if filter2 is None or filter2.find('CLEAR') == 0 or filter2.strip() == '':
         filter2 = 'CLEAR'
 
     # Insure that tabname is full filename with fully expanded
@@ -51,7 +48,7 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
     try:
         ftab = fileutil.openImage(tabname)
     except:
-        err_str =  "------------------------------------------------------------------------ \n"
+        err_str = "------------------------------------------------------------------------ \n"
         err_str += "WARNING: the IDCTAB geometric distortion file specified in the image     \n"
         err_str += "header was not found on disk. Please verify that your environment        \n"
         err_str += "variable ('jref'/'uref'/'oref'/'nref') has been correctly defined. If    \n"
@@ -63,7 +60,7 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
         err_str += "------------------------------------------------------------------------ \n"
         raise IOError(err_str)
 
-    #First thing we need, is to read in the coefficients from the IDC
+    # First thing we need, is to read in the coefficients from the IDC
     # table and populate the Fx and Fy matrices.
 
     if 'DETECTOR' in ftab['PRIMARY'].header:
@@ -96,10 +93,10 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
     else:
         order = norder
 
-    fx = np.zeros(shape=(order+1,order+1),dtype=np.float64)
-    fy = np.zeros(shape=(order+1,order+1),dtype=np.float64)
+    fx = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
+    fy = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
 
-    #Determine row from which to get the coefficients.
+    # Determine row from which to get the coefficients.
     # How many rows do we have in the table...
     fshape = ftab[1].data.shape
     colnames = ftab[1].data.names
@@ -111,14 +108,14 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
 
         try:
             # Match FILTER combo to appropriate row,
-            #if there is a filter column in the IDCTAB...
+            # if there is a filter column in the IDCTAB...
             if 'FILTER1' in colnames and 'FILTER2' in colnames:
 
                 filt1 = ftab[1].data.field('FILTER1')[i]
-                if filt1.find('CLEAR') > -1: filt1 = filt1[:5]
+                if filt1.find('CLEAR') > -1: filt1 = filt1[: 5]
 
                 filt2 = ftab[1].data.field('FILTER2')[i]
-                if filt2.find('CLEAR') > -1: filt2 = filt2[:5]
+                if filt2.find('CLEAR') > -1: filt2 = filt2[: 5]
             else:
                 if 'OPT_ELEM' in colnames:
                     filt1 = ftab[1].data.field('OPT_ELEM')
@@ -170,16 +167,17 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
         joinstr = ''
     else:
         f2str = filter2.strip()
-    filtstr = (joinstr.join([f1str,f2str])).strip()
+    filtstr = (joinstr.join([f1str, f2str])).strip()
     if row < 0:
         err_str = '\nProblem finding row in IDCTAB! Could not find row matching:\n'
-        err_str += '        CHIP: '+str(detchip)+'\n'
-        err_str += '     FILTERS: '+filtstr+'\n'
+        err_str += '        CHIP: ' + str(detchip) + '\n'
+        err_str += '     FILTERS: ' + filtstr + '\n'
         ftab.close()
         del ftab
         raise LookupError(err_str)
     else:
-        print('- IDCTAB: Distortion model from row',str(row+1),'for chip',detchip,':',filtstr)
+        print('- IDCTAB: Distortion model from row', str(row + 1), 'for chip',
+              detchip, ':', filtstr)
 
     # Read in V2REF and V3REF: this can either come from current table,
     # or from an OFFTAB if time-dependent (i.e., for WFPC2)
@@ -190,12 +188,12 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
     else:
         # Read V2REF/V3REF from offset table (OFFTAB)
         if offtab:
-            v2ref,v3ref,theta = readOfftab(offtab, date, chip=detchip)
+            v2ref, v3ref, theta = readOfftab(offtab, date, chip=detchip)
         else:
             v2ref = 0.0
             v3ref = 0.0
 
-    if theta == None:
+    if theta is None:
         if 'THETA' in colnames:
             theta = ftab[1].data.field('THETA')[row]
         else:
@@ -206,14 +204,14 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
     refpix['YREF'] = ftab[1].data.field('YREF')[row]
     refpix['XSIZE'] = ftab[1].data.field('XSIZE')[row]
     refpix['YSIZE'] = ftab[1].data.field('YSIZE')[row]
-    refpix['PSCALE'] = round(ftab[1].data.field('SCALE')[row],8)
+    refpix['PSCALE'] = round(ftab[1].data.field('SCALE')[row], 8)
     refpix['V2REF'] = v2ref
     refpix['V3REF'] = v3ref
     refpix['THETA'] = theta
     refpix['XDELTA'] = 0.0
     refpix['YDELTA'] = 0.0
-    refpix['DEFAULT_SCALE'] = yes
-    refpix['centered'] = no
+    refpix['DEFAULT_SCALE'] = True
+    refpix['centered'] = False
     refpix['skew_coeffs'] = skew_coeffs
     # Now that we know which row to look at, read coefficients into the
     #   numeric arrays we have set up...
@@ -226,13 +224,13 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
         cxstr = 'A'
         cystr = 'B'
 
-    for i in range(norder+1):
+    for i in range(norder + 1):
         if i > 0:
-            for j in range(i+1):
-                xcname = cxstr+str(i)+str(j)
-                ycname = cystr+str(i)+str(j)
-                fx[i,j] = ftab[1].data.field(xcname)[row]
-                fy[i,j] = ftab[1].data.field(ycname)[row]
+            for j in range(i + 1):
+                xcname = cxstr + str(i) + str(j)
+                ycname = cystr + str(i) + str(j)
+                fx[i, j] = ftab[1].data.field(xcname)[row]
+                fy[i, j] = ftab[1].data.field(ycname)[row]
 
     ftab.close()
     del ftab
@@ -240,21 +238,21 @@ def readIDCtab (tabname, chip=1, date=None, direction='forward',
     # If CX11 is 1.0 and not equal to the PSCALE, then the
     # coeffs need to be scaled
 
-    if fx[1,1] == 1.0 and abs(fx[1,1]) != refpix['PSCALE']:
+    if fx[1, 1] == 1.0 and abs(fx[1, 1]) != refpix['PSCALE']:
         fx *= refpix['PSCALE']
         fy *= refpix['PSCALE']
 
     # Return arrays and polynomial order read in from table.
     # NOTE: XREF and YREF are stored in Fx,Fy arrays respectively.
-    return fx,fy,refpix,order
-#
-#
-# Time-dependent skew correction coefficients (only ACS/WFC)
-#
-#
+    return fx, fy, refpix, order
+
+
 def read_tdd_coeffs(phdr, chip=1):
-    ''' Read in the TDD related keywords from the PRIMARY header of the IDCTAB
-    '''
+    """
+    Time-dependent skew correction coefficients (only ACS/WFC).
+
+    Read in the TDD related keywords from the PRIMARY header of the IDCTAB
+    """
     # Insure we have an integer form of chip
     ic = int(chip)
 
@@ -269,7 +267,7 @@ def read_tdd_coeffs(phdr, chip=1):
     skew_coeffs['TDD_CX_ALPHA'] = None
 
     # Skew-based TDD coefficients
-    skew_terms = ['TDD_CTB','TDD_CTA','TDD_CYA','TDD_CYB','TDD_CXA','TDD_CXB']
+    skew_terms = ['TDD_CTB', 'TDD_CTA', 'TDD_CYA', 'TDD_CYB', 'TDD_CXA', 'TDD_CXB']
     for s in skew_terms:
         skew_coeffs[s] = None
 
@@ -280,7 +278,7 @@ def read_tdd_coeffs(phdr, chip=1):
         print("Using 2015-calibrated VAFACTOR-corrected TDD correction...")
         skew_coeffs['TDD_DATE'] = phdr['TDD_DATE']
         for s in skew_terms:
-            skew_coeffs[s] = phdr.get('{0}{1}'.format(s,ic),None)
+            skew_coeffs[s] = phdr.get('{0}{1}'.format(s, ic), None)
 
     elif "TDD_CYB1" in phdr:
         # We have 2014-calibrated TDD correction to apply, not J.A.-derived values
@@ -288,17 +286,17 @@ def read_tdd_coeffs(phdr, chip=1):
         skew_coeffs['TDD_DATE'] = phdr['TDD_DATE']
         # Read coefficients for TDD Y coefficient
         cyb_kw = 'TDD_CYB{0}'.format(int(chip))
-        skew_coeffs['TDD_CY_BETA'] = phdr.get(cyb_kw,None)
+        skew_coeffs['TDD_CY_BETA'] = phdr.get(cyb_kw, None)
         cya_kw = 'TDD_CYA{0}'.format(int(chip))
-        tdd_cya = phdr.get(cya_kw,None)
+        tdd_cya = phdr.get(cya_kw, None)
         if tdd_cya == 0 or tdd_cya == 'N/A': tdd_cya = None
         skew_coeffs['TDD_CY_ALPHA'] = tdd_cya
 
         # Read coefficients for TDD X coefficient
         cxb_kw = 'TDD_CXB{0}'.format(int(chip))
-        skew_coeffs['TDD_CX_BETA'] = phdr.get(cxb_kw,None)
+        skew_coeffs['TDD_CX_BETA'] = phdr.get(cxb_kw, None)
         cxa_kw = 'TDD_CXA{0}'.format(int(chip))
-        tdd_cxa = phdr.get(cxa_kw,None)
+        tdd_cxa = phdr.get(cxa_kw, None)
         if tdd_cxa == 0 or tdd_cxa == 'N/A': tdd_cxa = None
         skew_coeffs['TDD_CX_ALPHA'] = tdd_cxa
 
@@ -309,12 +307,12 @@ def read_tdd_coeffs(phdr, chip=1):
             print('TDDORDER kw not present, using default TDD correction')
             return None
 
-        a = np.zeros((n+1,), np.float64)
-        b = np.zeros((n+1,), np.float64)
-        for i in range(n+1):
+        a = np.zeros((n + 1,), np.float64)
+        b = np.zeros((n + 1,), np.float64)
+        for i in range(n + 1):
             a[i] = phdr.get(("TDD_A%d" % i), 0.0)
             b[i] = phdr.get(("TDD_B%d" % i), 0.0)
-        if (a==0).all() and (b==0).all():
+        if (a == 0).all() and (b == 0).all():
             print('Warning: TDD_A and TDD_B coeffiecients have values of 0, \n \
                    but TDDORDER is %d.' % TDDORDER)
 
@@ -325,15 +323,15 @@ def read_tdd_coeffs(phdr, chip=1):
 
     return skew_coeffs
 
-def readOfftab(offtab, date, chip=None):
-
 
-#Read V2REF,V3REF from a specified offset table (OFFTAB).
-# Return a default geometry model if no IDCTAB filenam  e
-# is given.  This model will not distort the data in any way.
-
-    if offtab == None:
-        return 0.,0.
+def readOfftab(offtab, date, chip=None):
+    """
+    Read V2REF,V3REF from a specified offset table (OFFTAB).
+    Return a default geometry model if no IDCTAB filenam  e
+    is given.  This model will not distort the data in any way.
+    """
+    if offtab is None:
+        return 0., 0.
 
     # Provide a default value for chip
     if chip:
@@ -347,7 +345,7 @@ def readOfftab(offtab, date, chip=None):
     except:
         raise IOError("Offset table '%s' not valid as specified!" % offtab)
 
-    #Determine row from which to get the coefficients.
+    # Determine row from which to get the coefficients.
     # How many rows do we have in the table...
     fshape = ftab[1].data.shape
     colnames = ftab[1].data.names
@@ -374,7 +372,7 @@ def readOfftab(offtab, date, chip=None):
         obsdate = convertDate(ftab[1].data.field('OBSDATE')[i])
 
         # If the row is appropriate for the chip...
-            # Interpolate between dates
+        # Interpolate between dates
         if int(detchip) == int(chip) or int(detchip) == -999:
             if num_date <= obsdate:
                 date_end = obsdate
@@ -384,7 +382,7 @@ def readOfftab(offtab, date, chip=None):
                 row_end = i
                 continue
 
-            if row_end == None and (num_date > obsdate):
+            if row_end is None and (num_date > obsdate):
                 date_end = obsdate
                 v2end = ftab[1].data.field('V2REF')[i]
                 v3end = ftab[1].data.field('V3REF')[i]
@@ -403,16 +401,17 @@ def readOfftab(offtab, date, chip=None):
     ftab.close()
     del ftab
 
-    if row_start == None and row_end == None:
-        print('Row corresponding to DETCHIP of ',detchip,' was not found!')
+    if row_start is None and row_end is None:
+        print('Row corresponding to DETCHIP of ', detchip, ' was not found!')
         raise LookupError
-    elif row_start == None:
-        print('- OFFTAB: Offset defined by row',str(row_end+1))
+    elif row_start is None:
+        print('- OFFTAB: Offset defined by row', str(row_end + 1))
     else:
-        print('- OFFTAB: Offset interpolated from rows',str(row_start+1),'and',str(row_end+1))
+        print('- OFFTAB: Offset interpolated from rows', str(row_start + 1),
+              'and', str(row_end + 1))
 
     # Now, do the interpolation for v2ref, v3ref, and theta
-    if row_start == None or row_end == row_start:
+    if row_start is None or row_end is row_start:
         # We are processing an observation taken after the last calibration
         date_start = date_end
         v2start = v2end
@@ -426,31 +425,32 @@ def readOfftab(offtab, date, chip=None):
     v3ref = _fraction * (v3end - v3start) + v3start
     theta = _fraction * (theta_end - theta_start) + theta_start
 
-    return v2ref,v3ref,theta
+    return v2ref, v3ref, theta
 
-def readWCSCoeffs(header):
-
-    #Read distortion coeffs from WCS header keywords and
-    #populate distortion coeffs arrays.
 
+def readWCSCoeffs(header):
+    """
+    Read distortion coeffs from WCS header keywords and
+    populate distortion coeffs arrays.
+    """
     # Read in order for polynomials
     _xorder = header['a_order']
     _yorder = header['b_order']
-    order = max(max(_xorder,_yorder),3)
+    order = max(max(_xorder, _yorder), 3)
 
-    fx = np.zeros(shape=(order+1,order+1),dtype=np.float64)
-    fy = np.zeros(shape=(order+1,order+1),dtype=np.float64)
+    fx = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
+    fy = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
 
     # Read in CD matrix
     _cd11 = header['cd1_1']
     _cd12 = header['cd1_2']
     _cd21 = header['cd2_1']
     _cd22 = header['cd2_2']
-    _cdmat = np.array([[_cd11,_cd12],[_cd21,_cd22]])
-    _theta = np.arctan2(-_cd12,_cd22)
-    _rotmat = np.array([[np.cos(_theta),np.sin(_theta)],
-                      [-np.sin(_theta),np.cos(_theta)]])
-    _rCD = np.dot(_rotmat,_cdmat)
+    _cdmat = np.array([[_cd11, _cd12], [_cd21, _cd22]])
+    _theta = np.arctan2(-_cd12, _cd22)
+    _rotmat = np.array([[np.cos(_theta), np.sin(_theta)],
+                        [-np.sin(_theta), np.cos(_theta)]])
+    _rCD = np.dot(_rotmat, _cdmat)
     _skew = np.arcsin(-_rCD[1][0] / _rCD[0][0])
     _scale = _rCD[0][0] * np.cos(_skew) * 3600.
     _scale2 = _rCD[1][1] * 3600.
@@ -467,40 +467,40 @@ def readWCSCoeffs(header):
     refpix['THETA'] = np.rad2deg(_theta)
     refpix['XDELTA'] = 0.0
     refpix['YDELTA'] = 0.0
-    refpix['DEFAULT_SCALE'] = yes
-    refpix['centered'] = yes
-
+    refpix['DEFAULT_SCALE'] = True
+    refpix['centered'] = True
 
     # Set up template for coeffs keyword names
     cxstr = 'A_'
     cystr = 'B_'
     # Read coeffs into their own matrix
-    for i in range(_xorder+1):
-        for j in range(i+1):
-            xcname = cxstr+str(j)+'_'+str(i-j)
+    for i in range(_xorder + 1):
+        for j in range(i + 1):
+            xcname = cxstr + str(j) + '_' + str(i - j)
             if xcname in header:
-                fx[i,j] = header[xcname]
+                fx[i, j] = header[xcname]
 
     # Extract Y coeffs separately as a different order may
     # have been used to fit it.
-    for i in range(_yorder+1):
-        for j in range(i+1):
-            ycname = cystr+str(j)+'_'+str(i-j)
+    for i in range(_yorder + 1):
+        for j in range(i + 1):
+            ycname = cystr + str(j) + '_' + str(i - j)
             if ycname in header:
-                fy[i,j] = header[ycname]
+                fy[i, j] = header[ycname]
 
     # Now set the linear terms
     fx[0][0] = 1.0
     fy[0][0] = 1.0
 
-    return fx,fy,refpix,order
+    return fx, fy, refpix, order
 
 
-def readTraugerTable(idcfile,wavelength):
-
-    # Return a default geometry model if no coefficients filename
-    # is given.  This model will not distort the data in any way.
-    if idcfile == None:
+def readTraugerTable(idcfile, wavelength):
+    """
+    Return a default geometry model if no coefficients filename
+    is given.  This model will not distort the data in any way.
+    """
+    if idcfile is None:
         return fileutil.defaultModel()
 
     # Trauger coefficients only result in a cubic file...
@@ -510,10 +510,10 @@ def readTraugerTable(idcfile,wavelength):
     b_coeffs = [0] * numco
     indx = _MgF2(wavelength)
 
-    ifile = open(idcfile,'r')
+    ifile = open(idcfile, 'r')
     # Search for the first line of the coefficients
     _line = fileutil.rAsciiLine(ifile)
-    while _line[:7].lower() != 'trauger':
+    while _line[: 7].lower() != 'trauger':
         _line = fileutil.rAsciiLine(ifile)
     # Read in each row of coefficients,split them into their values,
     # and convert them into cubic coefficients based on
@@ -525,9 +525,11 @@ def readTraugerTable(idcfile,wavelength):
         if _line == '': continue
         _lc = _line.split()
         if j < 10:
-            a_coeffs[j] = float(_lc[0])+float(_lc[1])*(indx-1.5)+float(_lc[2])*(indx-1.5)**2
+            a_coeffs[j] = float(_lc[0]) + float(_lc[1]) * (indx - 1.5) + \
+                float(_lc[2]) * (indx - 1.5) ** 2
         else:
-            b_coeffs[j-10] = float(_lc[0])+float(_lc[1])*(indx-1.5)+float(_lc[2])*(indx-1.5)**2
+            b_coeffs[j - 10] = float(_lc[0]) + float(_lc[1]) * (indx - 1.5) + \
+                float(_lc[2]) * (indx - 1.5) ** 2
         j = j + 1
 
     ifile.close()
@@ -536,17 +538,17 @@ def readTraugerTable(idcfile,wavelength):
     # Now, convert the coefficients into a Numeric array
     # with the right coefficients in the right place.
     # Populate output values now...
-    fx = np.zeros(shape=(order+1,order+1),dtype=np.float64)
-    fy = np.zeros(shape=(order+1,order+1),dtype=np.float64)
+    fx = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
+    fy = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
     # Assign the coefficients to their array positions
-    fx[0,0] = 0.
-    fx[1] = np.array([a_coeffs[2],a_coeffs[1],0.,0.],dtype=np.float64)
-    fx[2] = np.array([a_coeffs[5],a_coeffs[4],a_coeffs[3],0.],dtype=np.float64)
-    fx[3] = np.array([a_coeffs[9],a_coeffs[8],a_coeffs[7],a_coeffs[6]],dtype=np.float64)
-    fy[0,0] = 0.
-    fy[1] = np.array([b_coeffs[2],b_coeffs[1],0.,0.],dtype=np.float64)
-    fy[2] = np.array([b_coeffs[5],b_coeffs[4],b_coeffs[3],0.],dtype=np.float64)
-    fy[3] = np.array([b_coeffs[9],b_coeffs[8],b_coeffs[7],b_coeffs[6]],dtype=np.float64)
+    fx[0, 0] = 0.
+    fx[1] = np.array([a_coeffs[2], a_coeffs[1], 0., 0.], dtype=np.float64)
+    fx[2] = np.array([a_coeffs[5], a_coeffs[4], a_coeffs[3], 0.], dtype=np.float64)
+    fx[3] = np.array([a_coeffs[9], a_coeffs[8], a_coeffs[7], a_coeffs[6]], dtype=np.float64)
+    fy[0, 0] = 0.
+    fy[1] = np.array([b_coeffs[2], b_coeffs[1], 0., 0.], dtype=np.float64)
+    fy[2] = np.array([b_coeffs[5], b_coeffs[4], b_coeffs[3], 0.], dtype=np.float64)
+    fy[3] = np.array([b_coeffs[9], b_coeffs[8], b_coeffs[7], b_coeffs[6]], dtype=np.float64)
 
     # Used in Pattern.computeOffsets()
     refpix = {}
@@ -557,10 +559,10 @@ def readTraugerTable(idcfile,wavelength):
     refpix['XDELTA'] = 0.
     refpix['YDELTA'] = 0.
     refpix['PSCALE'] = None
-    refpix['DEFAULT_SCALE'] = no
-    refpix['centered'] = yes
+    refpix['DEFAULT_SCALE'] = False
+    refpix['centered'] = True
 
-    return fx,fy,refpix,order
+    return fx, fy, refpix, order
 
 
 def readCubicTable(idcfile):
@@ -572,17 +574,17 @@ def readCubicTable(idcfile):
 
     # Return a default geometry model if no coefficients filename
     # is given.  This model will not distort the data in any way.
-    if idcfile == None:
+    if idcfile is None:
         return fileutil.defaultModel()
 
-    ifile = open(idcfile,'r')
+    ifile = open(idcfile, 'r')
     # Search for the first line of the coefficients
     _line = fileutil.rAsciiLine(ifile)
 
-    _found = no
-    while _found == no:
-        if _line[:7] in  ['cubic','quartic','quintic'] or _line[:4] == 'poly':
-            found = yes
+    _found = False
+    while not _found:
+        if _line[:7] in ['cubic', 'quartic', 'quintic'] or _line[: 4] == 'poly':
+            found = True
             break
         _line = fileutil.rAsciiLine(ifile)
 
@@ -613,17 +615,17 @@ def readCubicTable(idcfile):
     # Now, convert the coefficients into a Numeric array
     # with the right coefficients in the right place.
     # Populate output values now...
-    fx = np.zeros(shape=(order+1,order+1),dtype=np.float64)
-    fy = np.zeros(shape=(order+1,order+1),dtype=np.float64)
+    fx = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
+    fy = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
     # Assign the coefficients to their array positions
-    fx[0,0] = 0.
-    fx[1] = np.array([a_coeffs[2],a_coeffs[1],0.,0.],dtype=np.float64)
-    fx[2] = np.array([a_coeffs[5],a_coeffs[4],a_coeffs[3],0.],dtype=np.float64)
-    fx[3] = np.array([a_coeffs[9],a_coeffs[8],a_coeffs[7],a_coeffs[6]],dtype=np.float64)
-    fy[0,0] = 0.
-    fy[1] = np.array([b_coeffs[2],b_coeffs[1],0.,0.],dtype=np.float64)
-    fy[2] = np.array([b_coeffs[5],b_coeffs[4],b_coeffs[3],0.],dtype=np.float64)
-    fy[3] = np.array([b_coeffs[9],b_coeffs[8],b_coeffs[7],b_coeffs[6]],dtype=np.float64)
+    fx[0, 0] = 0.
+    fx[1] = np.array([a_coeffs[2], a_coeffs[1], 0., 0.], dtype=np.float64)
+    fx[2] = np.array([a_coeffs[5], a_coeffs[4], a_coeffs[3], 0.], dtype=np.float64)
+    fx[3] = np.array([a_coeffs[9], a_coeffs[8], a_coeffs[7], a_coeffs[6]], dtype=np.float64)
+    fy[0, 0] = 0.
+    fy[1] = np.array([b_coeffs[2], b_coeffs[1], 0., 0.], dtype=np.float64)
+    fy[2] = np.array([b_coeffs[5], b_coeffs[4], b_coeffs[3], 0.], dtype=np.float64)
+    fy[3] = np.array([b_coeffs[9], b_coeffs[8], b_coeffs[7], b_coeffs[6]], dtype=np.float64)
 
     # Used in Pattern.computeOffsets()
     refpix = {}
@@ -634,21 +636,23 @@ def readCubicTable(idcfile):
     refpix['XDELTA'] = 0.
     refpix['YDELTA'] = 0.
     refpix['PSCALE'] = None
-    refpix['DEFAULT_SCALE'] = no
-    refpix['centered'] = yes
+    refpix['DEFAULT_SCALE'] = False
+    refpix['centered'] = True
+
+    return fx, fy, refpix, order
 
-    return fx,fy,refpix,order
 
 def factorial(n):
     """ Compute a factorial for integer n. """
     m = 1
     for i in range(int(n)):
-        m = m * (i+1)
+        m = m * (i + 1)
     return m
 
-def combin(j,n):
+
+def combin(j, n):
     """ Return the combinatorial factor for j in n."""
-    return (factorial(j) / (factorial(n) * factorial( (j-n) ) ) )
+    return (factorial(j) / (factorial(n) * factorial((j - n))))
 
 
 def defaultModel():
@@ -657,15 +661,15 @@ def defaultModel():
     """
     order = 3
 
-    fx = np.zeros(shape=(order+1,order+1),dtype=np.float64)
-    fy = np.zeros(shape=(order+1,order+1),dtype=np.float64)
+    fx = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
+    fy = np.zeros(shape=(order + 1, order + 1), dtype=np.float64)
 
-    fx[1,1] = 1.
-    fy[1,0] = 1.
+    fx[1, 1] = 1.
+    fy[1, 0] = 1.
 
     # Used in Pattern.computeOffsets()
     refpix = {}
-    refpix['empty_model'] = yes
+    refpix['empty_model'] = True
     refpix['XREF'] = None
     refpix['YREF'] = None
     refpix['V2REF'] = 0.
@@ -675,17 +679,20 @@ def defaultModel():
     refpix['XDELTA'] = 0.
     refpix['YDELTA'] = 0.
     refpix['PSCALE'] = None
-    refpix['DEFAULT_SCALE'] = no
+    refpix['DEFAULT_SCALE'] = False
     refpix['THETA'] = 0.
-    refpix['centered'] = yes
-    return fx,fy,refpix,order
+    refpix['centered'] = True
+    return fx, fy, refpix, order
+
 
-# Function to compute the index of refraction for MgF2 at
-# the specified wavelength for use with Trauger coefficients
 def _MgF2(lam):
-    _sig = pow((1.0e7/lam),2)
-    return np.sqrt(1.0 + 2.590355e10/(5.312993e10-_sig) +
-        4.4543708e9/(11.17083e9-_sig) + 4.0838897e5/(1.766361e5-_sig))
+    """
+    Function to compute the index of refraction for MgF2 at
+    the specified wavelength for use with Trauger coefficients
+    """
+    _sig = pow((1.0e7 / lam), 2)
+    return np.sqrt(1.0 + 2.590355e10 / (5.312993e10 - _sig) +
+                   4.4543708e9 / (11.17083e9 - _sig) + 4.0838897e5 / (1.766361e5 - _sig))
 
 
 def convertDate(date):
diff --git a/stwcs/distortion/utils.py b/stwcs/distortion/utils.py
index 4228f62..1baad3f 100644
--- a/stwcs/distortion/utils.py
+++ b/stwcs/distortion/utils.py
@@ -1,4 +1,4 @@
-from __future__ import division, print_function # confidence high
+from __future__ import absolute_import, division, print_function
 
 import os
 
@@ -6,11 +6,11 @@ import numpy as np
 from numpy import linalg
 from astropy import wcs as pywcs
 
-from stwcs import wcsutil
-from stwcs import updatewcs
+from .. import updatewcs
 from numpy import sqrt, arctan2
 from stsci.tools import fileutil
 
+
 def output_wcs(list_of_wcsobj, ref_wcs=None, owcs=None, undistort=True):
     """
     Create an output WCS.
@@ -33,63 +33,65 @@ def output_wcs(list_of_wcsobj, ref_wcs=None, owcs=None, undistort=True):
 
     # This new algorithm may not be strictly necessary, but it may be more
     # robust in handling regions near the poles or at 0h RA.
-    crval1,crval2 = computeFootprintCenter(fra_dec)
+    crval1, crval2 = computeFootprintCenter(fra_dec)
 
-    crval = np.array([crval1,crval2], dtype=np.float64) # this value is now zero-based
+    crval = np.array([crval1, crval2], dtype=np.float64)  # this value is now zero-based
     if owcs is None:
         if ref_wcs is None:
             ref_wcs = list_of_wcsobj[0].deepcopy()
         if undistort:
-            #outwcs = undistortWCS(ref_wcs)
+            # outwcs = undistortWCS(ref_wcs)
             outwcs = make_orthogonal_cd(ref_wcs)
         else:
             outwcs = ref_wcs.deepcopy()
         outwcs.wcs.crval = crval
         outwcs.wcs.set()
-        outwcs.pscale = sqrt(outwcs.wcs.cd[0,0]**2 + outwcs.wcs.cd[1,0]**2)*3600.
-        outwcs.orientat = arctan2(outwcs.wcs.cd[0,1],outwcs.wcs.cd[1,1]) * 180./np.pi
+        outwcs.pscale = sqrt(outwcs.wcs.cd[0, 0] ** 2 + outwcs.wcs.cd[1, 0] ** 2) * 3600.
+        outwcs.orientat = arctan2(outwcs.wcs.cd[0, 1], outwcs.wcs.cd[1, 1]) * 180. / np.pi
     else:
         outwcs = owcs.deepcopy()
-        outwcs.pscale = sqrt(outwcs.wcs.cd[0,0]**2 + outwcs.wcs.cd[1,0]**2)*3600.
-        outwcs.orientat = arctan2(outwcs.wcs.cd[0,1],outwcs.wcs.cd[1,1]) * 180./np.pi
+        outwcs.pscale = sqrt(outwcs.wcs.cd[0, 0] ** 2 + outwcs.wcs.cd[1, 0] ** 2) * 3600.
+        outwcs.orientat = arctan2(outwcs.wcs.cd[0, 1], outwcs.wcs.cd[1, 1]) * 180. / np.pi
 
     tanpix = outwcs.wcs.s2p(fra_dec, 0)['pixcrd']
 
-    outwcs._naxis1 = int(np.ceil(tanpix[:,0].max() - tanpix[:,0].min()))
-    outwcs._naxis2 = int(np.ceil(tanpix[:,1].max() - tanpix[:,1].min()))
-    crpix = np.array([outwcs._naxis1/2., outwcs._naxis2/2.], dtype=np.float64)
+    outwcs._naxis1 = int(np.ceil(tanpix[:, 0].max() - tanpix[:, 0].min()))
+    outwcs._naxis2 = int(np.ceil(tanpix[:, 1].max() - tanpix[:, 1].min()))
+    crpix = np.array([outwcs._naxis1 / 2., outwcs._naxis2 / 2.], dtype=np.float64)
     outwcs.wcs.crpix = crpix
     outwcs.wcs.set()
     tanpix = outwcs.wcs.s2p(fra_dec, 0)['pixcrd']
 
     # shift crpix to take into account (floating-point value of) position of
     # corner pixel relative to output frame size: no rounding necessary...
-    newcrpix = np.array([crpix[0]+tanpix[:,0].min(), crpix[1]+
-                         tanpix[:,1].min()])
+    newcrpix = np.array([crpix[0] + tanpix[:, 0].min(), crpix[1] +
+                         tanpix[:, 1].min()])
 
     newcrval = outwcs.wcs.p2s([newcrpix], 1)['world'][0]
     outwcs.wcs.crval = newcrval
     outwcs.wcs.set()
-    outwcs.wcs.name = wcsname # keep track of label for this solution
+    outwcs.wcs.name = wcsname  # keep track of label for this solution
     return outwcs
 
+
 def computeFootprintCenter(edges):
     """ Geographic midpoint in spherical coords for points defined by footprints.
         Algorithm derived from: http://www.geomidpoint.com/calculation.html
 
         This algorithm should be more robust against discontinuities at the poles.
     """
-    alpha = np.deg2rad(edges[:,0])
-    dec = np.deg2rad(edges[:,1])
+    alpha = np.deg2rad(edges[:, 0])
+    dec = np.deg2rad(edges[:, 1])
 
-    xmean = np.mean(np.cos(dec)*np.cos(alpha))
-    ymean = np.mean(np.cos(dec)*np.sin(alpha))
+    xmean = np.mean(np.cos(dec) * np.cos(alpha))
+    ymean = np.mean(np.cos(dec) * np.sin(alpha))
     zmean = np.mean(np.sin(dec))
 
-    crval1 = np.rad2deg(np.arctan2(ymean,xmean))%360.0
-    crval2 = np.rad2deg(np.arctan2(zmean,np.sqrt(xmean*xmean+ymean*ymean)))
+    crval1 = np.rad2deg(np.arctan2(ymean, xmean)) % 360.0
+    crval2 = np.rad2deg(np.arctan2(zmean, np.sqrt(xmean * xmean + ymean * ymean)))
+
+    return crval1, crval2
 
-    return crval1,crval2
 
 def make_orthogonal_cd(wcs):
     """ Create a perfect (square, orthogonal, undistorted) CD matrix from the
@@ -98,21 +100,20 @@ def make_orthogonal_cd(wcs):
     # get determinant of the CD matrix:
     cd = wcs.celestial.pixel_scale_matrix
 
-
     if hasattr(wcs, 'idcv2ref') and wcs.idcv2ref is not None:
         # Convert the PA_V3 orientation to the orientation at the aperture
         # This is for the reference chip only - we use this for the
         # reference tangent plane definition
         # It has the same orientation as the reference chip
-        pv = updatewcs.makewcs.troll(wcs.pav3,wcs.wcs.crval[1],wcs.idcv2ref,wcs.idcv3ref)
+        pv = updatewcs.makewcs.troll(wcs.pav3, wcs.wcs.crval[1], wcs.idcv2ref, wcs.idcv3ref)
         # Add the chip rotation angle
         if wcs.idctheta:
             pv += wcs.idctheta
         cs = np.cos(np.deg2rad(pv))
         sn = np.sin(np.deg2rad(pv))
-        pvmat = np.dot(np.array([[cs,sn],[-sn,cs]]),wcs.parity)
-        rot = np.arctan2(pvmat[0,1],pvmat[1,1])
-        scale = wcs.idcscale/3600.
+        pvmat = np.dot(np.array([[cs, sn], [-sn, cs]]), wcs.parity)
+        rot = np.arctan2(pvmat[0, 1], pvmat[1, 1])
+        scale = wcs.idcscale / 3600.
 
         det = linalg.det(wcs.parity)
 
@@ -122,36 +123,37 @@ def make_orthogonal_cd(wcs):
 
         # find pixel scale:
         if hasattr(wcs, 'idcscale'):
-            scale = (wcs.idcscale) / 3600. # HST pixel scale provided
+            scale = (wcs.idcscale) / 3600.  # HST pixel scale provided
         else:
-            scale = np.sqrt(np.abs(det)) # find as sqrt(pixel area)
+            scale = np.sqrt(np.abs(det))  # find as sqrt(pixel area)
 
         # find Y-axis orientation:
         if hasattr(wcs, 'orientat') and not ignoreHST:
-            rot = np.deg2rad(wcs.orientat) # use HST ORIENTAT
+            rot = np.deg2rad(wcs.orientat)  # use HST ORIENTAT
         else:
-            rot = np.arctan2(wcs.wcs.cd[0,1], wcs.wcs.cd[1,1]) # angle of the Y-axis
+            rot = np.arctan2(wcs.wcs.cd[0, 1], wcs.wcs.cd[1, 1])  # angle of the Y-axis
 
     par = -1 if det < 0.0 else 1
 
     # create a perfectly square, orthogonal WCS
     sn = np.sin(rot)
     cs = np.cos(rot)
-    orthogonal_cd = scale * np.array([[par*cs, sn], [-par*sn, cs]])
+    orthogonal_cd = scale * np.array([[par * cs, sn], [-par * sn, cs]])
 
     lin_wcsobj = pywcs.WCS()
     lin_wcsobj.wcs.cd = orthogonal_cd
     lin_wcsobj.wcs.set()
-    lin_wcsobj.orientat = arctan2(lin_wcsobj.wcs.cd[0,1],lin_wcsobj.wcs.cd[1,1]) * 180./np.pi
-    lin_wcsobj.pscale = sqrt(lin_wcsobj.wcs.cd[0,0]**2 + lin_wcsobj.wcs.cd[1,0]**2)*3600.
-    lin_wcsobj.wcs.crval = np.array([0.,0.])
-    lin_wcsobj.wcs.crpix = np.array([0.,0.])
+    lin_wcsobj.orientat = arctan2(lin_wcsobj.wcs.cd[0, 1], lin_wcsobj.wcs.cd[1, 1]) * 180. / np.pi
+    lin_wcsobj.pscale = sqrt(lin_wcsobj.wcs.cd[0, 0] ** 2 + lin_wcsobj.wcs.cd[1, 0] ** 2) * 3600.
+    lin_wcsobj.wcs.crval = np.array([0., 0.])
+    lin_wcsobj.wcs.crpix = np.array([0., 0.])
     lin_wcsobj.wcs.ctype = ['RA---TAN', 'DEC--TAN']
     lin_wcsobj.wcs.set()
 
     return lin_wcsobj
 
-def  undistortWCS(wcsobj):
+
+def undistortWCS(wcsobj):
     """
     Creates an undistorted linear WCS by applying the IDCTAB distortion model
     to a 3-point square. The new ORIENTAT angle is calculated as well as the
@@ -175,25 +177,26 @@ def  undistortWCS(wcsobj):
             return wcsobj.copy()
     crpix1 = wcsobj.wcs.crpix[0]
     crpix2 = wcsobj.wcs.crpix[1]
-    xy = np.array([(crpix1,crpix2),(crpix1+1.,crpix2),(crpix1,crpix2+1.)],dtype=np.double)
+    xy = np.array([(crpix1, crpix2), (crpix1 + 1., crpix2),
+                   (crpix1, crpix2 + 1.)], dtype=np.double)
     offsets = np.array([wcsobj.ltv1, wcsobj.ltv2])
     px = xy + offsets
-    #order = wcsobj.sip.a_order
+    # order = wcsobj.sip.a_order
     pscale = wcsobj.idcscale
-    #pixref = np.array([wcsobj.sip.SIPREF1, wcsobj.sip.SIPREF2])
+    # pixref = np.array([wcsobj.sip.SIPREF1, wcsobj.sip.SIPREF2])
 
     tan_pix = apply_idc(px, cx, cy, wcsobj.wcs.crpix, pscale, order=1)
-    xc = tan_pix[:,0]
-    yc = tan_pix[:,1]
+    xc = tan_pix[:, 0]
+    yc = tan_pix[:, 1]
     am = xc[1] - xc[0]
     bm = xc[2] - xc[0]
     cm = yc[1] - yc[0]
     dm = yc[2] - yc[0]
-    cd_mat = np.array([[am,bm],[cm,dm]],dtype=np.double)
+    cd_mat = np.array([[am, bm], [cm, dm]], dtype=np.double)
 
     # Check the determinant for singularity
     _det = (am * dm) - (bm * cm)
-    if ( _det == 0.0):
+    if (_det == 0.0):
         print('Singular matrix in updateWCS, aborting ...')
         return
 
@@ -202,15 +205,16 @@ def  undistortWCS(wcsobj):
     cd = np.dot(wcsobj.wcs.cd, cd_inv).astype(np.float64)
     lin_wcsobj.wcs.cd = cd
     lin_wcsobj.wcs.set()
-    lin_wcsobj.orientat = arctan2(lin_wcsobj.wcs.cd[0,1],lin_wcsobj.wcs.cd[1,1]) * 180./np.pi
-    lin_wcsobj.pscale = sqrt(lin_wcsobj.wcs.cd[0,0]**2 + lin_wcsobj.wcs.cd[1,0]**2)*3600.
-    lin_wcsobj.wcs.crval = np.array([0.,0.])
-    lin_wcsobj.wcs.crpix = np.array([0.,0.])
+    lin_wcsobj.orientat = arctan2(lin_wcsobj.wcs.cd[0, 1], lin_wcsobj.wcs.cd[1, 1]) * 180. / np.pi
+    lin_wcsobj.pscale = sqrt(lin_wcsobj.wcs.cd[0, 0] ** 2 + lin_wcsobj.wcs.cd[1, 0] ** 2) * 3600.
+    lin_wcsobj.wcs.crval = np.array([0., 0.])
+    lin_wcsobj.wcs.crpix = np.array([0., 0.])
     lin_wcsobj.wcs.ctype = ['RA---TAN', 'DEC--TAN']
     lin_wcsobj.wcs.set()
     return lin_wcsobj
 
-def apply_idc(pixpos, cx, cy, pixref, pscale= None, order=None):
+
+def apply_idc(pixpos, cx, cy, pixref, pscale=None, order=None):
     """
     Apply the IDCTAB polynomial distortion model to pixel positions.
     pixpos must be already corrected for ltv1/2.
@@ -233,27 +237,28 @@ def apply_idc(pixpos, cx, cy, pixref, pscale= None, order=None):
         return pixpos
 
     # Apply in the same way that 'drizzle' would...
-    _cx = cx/pscale
-    _cy = cy/ pscale
+    _cx = cx / pscale
+    _cy = cy / pscale
     _p = pixpos
 
     # Do NOT include any zero-point terms in CX,CY here
     # as they should not be scaled by plate-scale like rest
     # of coeffs...  This makes the computations consistent
     # with 'drizzle'.  WJH 17-Feb-2004
-    _cx[0,0] = 0.
-    _cy[0,0] = 0.
+    _cx[0, 0] = 0.
+    _cy[0, 0] = 0.
 
     dxy = _p - pixref
     # Apply coefficients from distortion model here...
 
     c = _p * 0.
-    for i in range(order+1):
-        for j in range(i+1):
-            c[:,0] = c[:,0] + _cx[i][j] * pow(dxy[:,0],j) * pow(dxy[:,1],(i-j))
-            c[:,1] = c[:,1] + _cy[i][j] * pow(dxy[:,0],j) * pow(dxy[:,1],(i-j))
+    for i in range(order + 1):
+        for j in range(i + 1):
+            c[:, 0] = c[:, 0] + _cx[i][j] * pow(dxy[:, 0], j) * pow(dxy[:, 1], (i - j))
+            c[:, 1] = c[:, 1] + _cy[i][j] * pow(dxy[:, 0], j) * pow(dxy[:, 1], (i - j))
+
+    return c
 
-    return  c
 
 def foundIDCTAB(idctab):
     idctab_found = True
diff --git a/stwcs/gui/apply_headerlet.py b/stwcs/gui/apply_headerlet.py
index d517e9f..0cef612 100644
--- a/stwcs/gui/apply_headerlet.py
+++ b/stwcs/gui/apply_headerlet.py
@@ -1,31 +1,34 @@
+from __future__ import absolute_import, division, print_function
 import os
 from stsci.tools import teal, parseinput
 
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
-__taskname__ = __name__.split('.')[-1] # needed for help string
+__taskname__ = __name__.split('.')[-1]  # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
-#
-#### Interfaces used by TEAL
-#
+# __version__ = stwcs.__version__
+
+
+############### Interfaces used by TEAL ###############
+
 def getHelpAsString(docstring=False):
     """
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
     # start by interpreting filename and hdrlet inputs
@@ -37,18 +40,18 @@ def run(configObj=None):
         # Syntax: apply_headerlet_as_primary(filename, hdrlet, attach=True,
         #            archive=True, force=False, verbose=False)
         headerlet.apply_headerlet_as_primary(filename,
-                        hdrlet,attach=configObj['attach'],
-                        archive=configObj['archive'],force=configObj['force'],
-                        logging=configObj['logging'])
+                                             hdrlet, attach=configObj['attach'],
+                                             archive=configObj['archive'], force=configObj['force'],
+                                             logging=configObj['logging'])
     else:
         wcsname = configObj['wcsname']
-        if wcsname in ['',' ','INDEF']: wcsname = None
+        if wcsname in ['', ' ', 'INDEF']: wcsname = None
         wcskey = configObj['wcskey']
         if wcskey == '': wcskey = None
         # Call function with properly interpreted input parameters
         #         apply_headerlet_as_alternate(filename, hdrlet, attach=True,
         #                        wcskey=None, wcsname=None, verbose=False)
         headerlet.apply_headerlet_as_alternate(filename,
-                        hdrlet, attach=configObj['attach'],
-                        wcsname=wcsname, wcskey=wcskey,
-                        logging=configObj['logging'])
+                                               hdrlet, attach=configObj['attach'],
+                                               wcsname=wcsname, wcskey=wcskey,
+                                               logging=configObj['logging'])
diff --git a/stwcs/gui/archive_headerlet.py b/stwcs/gui/archive_headerlet.py
index 7ad3d4d..577a348 100644
--- a/stwcs/gui/archive_headerlet.py
+++ b/stwcs/gui/archive_headerlet.py
@@ -1,49 +1,49 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
 import os
 
-from astropy.io import fits
 from stsci.tools import teal
+from .. import __version__
+from ..wcsutil import headerlet
 
-import stwcs
-from stwcs.wcsutil import headerlet
-
-__taskname__ = __name__.split('.')[-1] # needed for help string
+__taskname__ = __name__.split('.')[-1]  # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+# __version__ = stwcs.__version__
+
 #
 #### Interfaces used by TEAL
 #
 def getHelpAsString(docstring=False):
     """
-    return useful help from a file in the script directory called __taskname__.help
+    Return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
             helpString += headerlet.archive_as_headerlet.__doc__
 
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
-    if configObj['hdrname'] in ['',' ','INDEF']:
-        print('='*60)
+    if configObj['hdrname'] in ['', ' ', 'INDEF']:
+        print('=' * 60)
         print('ERROR:')
         print('    No valid "hdrname" parameter value provided!')
         print('    Please restart this task and provide a value for this parameter.')
-        print('='*60)
+        print('=' * 60)
         return
 
-    str_kw = ['wcsname','destim','sipname','npolfile','d2imfile',
-            'descrip','history','author']
+    str_kw = ['wcsname', 'destim', 'sipname', 'npolfile', 'd2imfile',
+              'descrip', 'history', 'author']
 
     # create dictionary of remaining parameters, deleting extraneous ones
     # such as those above
@@ -66,4 +66,4 @@ def run(configObj=None):
     #                    author=None, descrip=None, history=None,
     #                    hdrlet=None, clobber=False)
     headerlet.archive_as_headerlet(configObj['filename'], configObj['hdrname'],
-                                **cdict)
+                                   **cdict)
diff --git a/stwcs/gui/attach_headerlet.py b/stwcs/gui/attach_headerlet.py
index 873c549..f3ab690 100644
--- a/stwcs/gui/attach_headerlet.py
+++ b/stwcs/gui/attach_headerlet.py
@@ -1,13 +1,13 @@
+from __future__ import absolute_import, division, print_function
 import os
 
 from stsci.tools import teal
+from .. import __version
+from ..wcsutil import headerlet
 
-import stwcs
-from stwcs.wcsutil import headerlet
-
-__taskname__ = __name__.split('.')[-1] # needed for help string
+__taskname__ = __name__.split('.')[-1]  # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+#__version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -16,21 +16,21 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
-            helpString += eval('.'.join([__package__,__taskname__,'__doc__']))
+            helpString += eval('.'.join([__package__, __taskname__, '__doc__']))
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
-    headerlet.attach_headerlet(configObj['filename'],configObj['hdrlet'],
+    headerlet.attach_headerlet(configObj['filename'], configObj['hdrlet'],
                                configObj['logging'])
-
diff --git a/stwcs/gui/delete_headerlet.py b/stwcs/gui/delete_headerlet.py
index b3df5a7..29937f7 100644
--- a/stwcs/gui/delete_headerlet.py
+++ b/stwcs/gui/delete_headerlet.py
@@ -1,15 +1,15 @@
-from __future__ import print_function
-import os
+from __future__ import absolute_import, division, print_function
 
+import os
 from stsci.tools import teal
 from stsci.tools import parseinput
 
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
-__taskname__ = __name__.split('.')[-1] # needed for help string
+__taskname__ = __name__.split('.')[-1]  # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+# __version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -18,35 +18,34 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
-            helpString += eval('.'.join([__package__,__taskname__,'__doc__']))
+            helpString += eval('.'.join([__package__, __taskname__, '__doc__']))
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
 def run(configObj=None):
 
     if configObj['hdrname'] == '' and configObj['hdrext'] is None and \
-        configObj['distname'] == '':
-        print('='*60)
+            configObj['distname'] == '':
+        print('=' * 60)
         print('ERROR:')
         print('    No valid "hdrname", "hdrext" or "distname" parameter value provided!')
         print('    Please restart this task and provide a value for one of these parameters.')
-        print('='*60)
+        print('=' * 60)
         return
     filename = parseinput.parseinput(configObj['filename'])[0]
     # Call function with properly interpreted input parameters
     # Syntax: delete_headerlet(filename, hdrname=None, hdrext=None, distname=None)
     headerlet.delete_headerlet(filename,
-                                hdrname = configObj['hdrname'],
-                                hdrext = configObj['hdrext'],
-                                distname = configObj['distname'],
-                                logging = configObj['logging'])
-
+                               hdrname=configObj['hdrname'],
+                               hdrext=configObj['hdrext'],
+                               distname=configObj['distname'],
+                               logging=configObj['logging'])
diff --git a/stwcs/gui/extract_headerlet.py b/stwcs/gui/extract_headerlet.py
index 02ecd7a..1e88221 100644
--- a/stwcs/gui/extract_headerlet.py
+++ b/stwcs/gui/extract_headerlet.py
@@ -1,14 +1,14 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
+
 import os
 
 from stsci.tools import teal
-
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
 __taskname__ = __name__.split('.')[-1] # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+# __version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -17,28 +17,29 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
-            helpString += eval('.'.join([__package__,__taskname__,'__doc__']))
+            helpString += eval('.'.join([__package__, __taskname__, '__doc__']))
 
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
-    if configObj['output'] in ['',' ',None]:
-        print('='*60)
+    if configObj['output'] in ['', ' ', None]:
+        print('=' * 60)
         print('ERROR:')
         print('    No valid "output" parameter value provided!')
         print('    Please restart this task and provide a value for this parameter.')
-        print('='*60)
+        print('=' * 60)
         return
 
     # create dictionary of remaining parameters, deleting extraneous ones
@@ -55,4 +56,3 @@ def run(configObj=None):
     #                clobber=False, verbose=100)
     headerlet.extract_headerlet(configObj['filename'], configObj['output'],
                                 **cdict)
-
diff --git a/stwcs/gui/headerlet_summary.py b/stwcs/gui/headerlet_summary.py
index 82a3e0c..eac59ee 100644
--- a/stwcs/gui/headerlet_summary.py
+++ b/stwcs/gui/headerlet_summary.py
@@ -1,12 +1,13 @@
+from __future__ import absolute_import, division, print_function
 import os
 from stsci.tools import teal
 
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
 __taskname__ = __name__.split('.')[-1] # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+# __version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -15,19 +16,20 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
-            helpString += eval('.'.join([__package__,__taskname__,'__doc__']))
+            helpString += eval('.'.join([__package__, __taskname__, '__doc__']))
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
     # create dictionary of remaining parameters, deleting extraneous ones
@@ -43,5 +45,4 @@ def run(configObj=None):
 
     # Syntax: headerlet_summary(filename,columns=None,pad=2,maxwidth=None,
     #                    output=None,clobber=True,quiet=False)
-    headerlet.headerlet_summary(configObj['filename'],**cdict)
-
+    headerlet.headerlet_summary(configObj['filename'], **cdict)
diff --git a/stwcs/gui/restore_headerlet.py b/stwcs/gui/restore_headerlet.py
index 7570d76..790c239 100644
--- a/stwcs/gui/restore_headerlet.py
+++ b/stwcs/gui/restore_headerlet.py
@@ -1,13 +1,14 @@
+from __future__ import absolute_import, division, print_function
 import os
 
 from stsci.tools import teal
 
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
 __taskname__ = __name__.split('.')[-1] # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+#__version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -16,33 +17,33 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
-    if configObj['distname'] not in ['',' ','INDEF']:
+    if configObj['distname'] not in ['', ' ', 'INDEF']:
         # Call function with properly interpreted input parameters
         # Syntax: restore_all_with_distname(filename, distname, primary,
         #           archive=True, sciext='SCI', verbose=False)
         headerlet.restore_all_with_distname(configObj['filename'],
-                        configObj['distname'],configObj['primary'],
-                        archive=configObj['archive'],sciext=configObj['sciext'],
-                        logging=configObj['logging'])
+                                            configObj['distname'], configObj['primary'],
+                                            archive=configObj['archive'], sciext=configObj['sciext'],
+                                            logging=configObj['logging'])
     else:
         # Call function with properly interpreted input parameters
         #         restore_from_headerlet(filename, hdrname=None, hdrext=None,
         #           archive=True, force=False)
         headerlet.restore_from_headerlet(configObj['filename'],
-                        hdrname=configObj['hdrname'],hdrext=configObj['hdrext'],
-                        archive=configObj['archive'], force=configObj['force'],
-                        logging=configObj['logging'])
-
+                                         hdrname=configObj['hdrname'], hdrext=configObj['hdrext'],
+                                         archive=configObj['archive'], force=configObj['force'],
+                                         logging=configObj['logging'])
diff --git a/stwcs/gui/updatewcs.py b/stwcs/gui/updatewcs.py
index 3dacb67..b5dc700 100644
--- a/stwcs/gui/updatewcs.py
+++ b/stwcs/gui/updatewcs.py
@@ -1,19 +1,22 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
+
 import os
 
 from astropy.io import fits
 from stsci.tools import parseinput
 from stsci.tools import fileutil
 from stsci.tools import teal
-import stwcs
-from stwcs import updatewcs
-from stwcs.wcsutil import convertwcs
+from .. import __version__
+from .. import updatewcs
+
+
+allowed_corr_dict = {'vacorr': 'VACorr', 'tddcorr': 'TDDCorr', 'npolcorr': 'NPOLCorr',
+                     'd2imcorr': 'DET2IMCorr'}
 
-allowed_corr_dict = {'vacorr':'VACorr','tddcorr':'TDDCorr','npolcorr':'NPOLCorr','d2imcorr':'DET2IMCorr'}
 
 __taskname__ = __name__.split('.')[-1] # needed for help string
 __package__ = updatewcs.__name__
-__version__ = stwcs.__version__
+#__version__ = stwcs.__version__
 
 #
 #### Interfaces used by TEAL
@@ -23,24 +26,24 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
-            helpString += eval('.'.join([__package__,__taskname__,'__doc__']))
+            helpString += eval('.'.join([__package__, __taskname__, '__doc__']))
 
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
 
     # Interpret primary parameters from configObj instance
-    extname = configObj['extname']
     input = configObj['input']
 
     # create dictionary of remaining parameters, deleting extraneous ones
@@ -53,7 +56,7 @@ def run(configObj=None):
     del cdict['extname']
 
     # parse input
-    input,altfiles = parseinput.parseinput(configObj['input'])
+    input, altfiles = parseinput.parseinput(configObj['input'])
 
     # Insure that all input files have a correctly archived
     #    set of OPUS WCS keywords
@@ -69,7 +72,7 @@ def run(configObj=None):
         # Check to insure that there is a valid reference file to be used
         idctab = fits.getval(file, 'idctab')
         if not os.path.exists(fileutil.osfn(idctab)):
-            print('No valid distortion reference file ',idctab,' found in ',file,'!')
+            print('No valid distortion reference file ', idctab, ' found in ', file, '!')
             raise ValueError
 
     # Re-define 'cdict' to only have switches for steps supported by that instrument
@@ -78,7 +81,7 @@ def run(configObj=None):
     #
     for file in input:
         # get instrument name from input file
-        instr = fits.getval(file,'INSTRUME')
+        instr = fits.getval(file, 'INSTRUME')
         # make copy of input parameters dict for this file
         fdict = cdict.copy()
         # Remove any parameter that is not part of this instrument's allowed corrections
@@ -86,5 +89,4 @@ def run(configObj=None):
             if allowed_corr_dict[step] not in updatewcs.apply_corrections.allowed_corrections[instr]:
                 fdict[step]
         # Call 'updatewcs' on correctly archived file
-        updatewcs.updatewcs(file,**fdict)
-
+        updatewcs.updatewcs(file, **fdict)
diff --git a/stwcs/gui/write_headerlet.py b/stwcs/gui/write_headerlet.py
index e18bed8..56520b3 100644
--- a/stwcs/gui/write_headerlet.py
+++ b/stwcs/gui/write_headerlet.py
@@ -1,15 +1,15 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
 import os
 
 from stsci.tools import teal
 from stsci.tools import parseinput
 
-import stwcs
-from stwcs.wcsutil import headerlet
+from .. import __version__
+from ..wcsutil import headerlet
 
 __taskname__ = __name__.split('.')[-1] # needed for help string
 __package__ = headerlet.__name__
-__version__ = stwcs.__version__
+#__version__ = stwcs.__version__
 #
 #### Interfaces used by TEAL
 #
@@ -18,43 +18,44 @@ def getHelpAsString(docstring=False):
     return useful help from a file in the script directory called __taskname__.help
     """
     install_dir = os.path.dirname(__file__)
-    htmlfile = os.path.join(install_dir,'htmlhelp',__taskname__+'.html')
-    helpfile = os.path.join(install_dir,__taskname__+'.help')
+    htmlfile = os.path.join(install_dir, 'htmlhelp', __taskname__ + '.html')
+    helpfile = os.path.join(install_dir, __taskname__ + '.help')
     if docstring or (not docstring and not os.path.exists(htmlfile)):
-        helpString = __taskname__+' Version '+__version__+'\n\n'
+        helpString = __taskname__ + ' Version ' + __version__ + '\n\n'
         if os.path.exists(helpfile):
-            helpString += teal.getHelpFileAsString(__taskname__,__file__)
+            helpString += teal.getHelpFileAsString(__taskname__, __file__)
         else:
             helpString += headerlet.write_headerlet.__doc__
 
     else:
-        helpString = 'file://'+htmlfile
+        helpString = 'file://' + htmlfile
 
     return helpString
 
+
 def run(configObj=None):
-    flist,oname = parseinput.parseinput(configObj['filename'])
+    flist, oname = parseinput.parseinput(configObj['filename'])
     if len(flist) == 0:
-        print('='*60)
+        print('=' * 60)
         print('ERROR:')
         print('    No valid "filename" parameter value provided!')
         print('    Please check the working directory and restart this task.')
-        print('='*60)
+        print('=' * 60)
         return
 
-    if configObj['hdrname'] in ['',' ','INDEF']:
-        print('='*60)
+    if configObj['hdrname'] in ['', ' ', 'INDEF']:
+        print('=' * 60)
         print('ERROR:')
         print('    No valid "hdrname" parameter value provided!')
         print('    Please restart this task and provide a value for this parameter.')
-        print('='*60)
+        print('=' * 60)
         return
 
-    if configObj['output'] in ['',' ','INDEF']:
+    if configObj['output'] in ['', ' ', 'INDEF']:
         configObj['output'] = None
 
-    str_kw = ['wcsname','destim','sipname','npolfile','d2imfile',
-            'descrip','history','author','output','catalog']
+    str_kw = ['wcsname', 'destim', 'sipname', 'npolfile', 'd2imfile',
+              'descrip', 'history', 'author', 'output', 'catalog']
 
     # create dictionary of remaining parameters, deleting extraneous ones
     # such as those above
diff --git a/stwcs/tests/test_altwcs.py b/stwcs/tests/test_altwcs.py
index 86d100f..d646106 100644
--- a/stwcs/tests/test_altwcs.py
+++ b/stwcs/tests/test_altwcs.py
@@ -1,11 +1,14 @@
+from __future__ import absolute_import, division, print_function
+
 import shutil
 import os
 from astropy.io import fits as pyfits
-from stwcs.wcsutil import altwcs
-from stwcs import updatewcs
-from stwcs.wcsutil import HSTWCS
+from ..wcsutil import altwcs
+from .. import updatewcs
+from .. import wcsutil
 import numpy as np
 from numpy.testing import utils
+import pytest
 
 from . import data
 data_path = os.path.split(os.path.abspath(data.__file__))[0]
@@ -70,25 +73,25 @@ class TestAltWCS(object):
         updatewcs.updatewcs(acs_file)
         self.acs_file = acs_file
         self.simplefits = simple_file
-        self.ww = HSTWCS(self.acs_file, ext=1)
+        self.ww = wcsutil.HSTWCS(self.acs_file, ext=1)
 
     def test_archive(self):
         altwcs.archiveWCS(self.acs_file, ext=1, wcskey='Z', wcsname='ZTEST', reusekey=False)
-        w1 = HSTWCS(self.acs_file, ext=1)
-        w1z = HSTWCS(self.acs_file, ext=1, wcskey='Z')
+        w1 = wcsutil.HSTWCS(self.acs_file, ext=1)
+        w1z = wcsutil.HSTWCS(self.acs_file, ext=1, wcskey='Z')
         compare_wcs(w1, w1z)
 
     def test_archive_clobber(self):
         altwcs.archiveWCS(self.acs_file, ext=1, wcskey='Z', wcsname='ZTEST', reusekey=True)
-        w1 = HSTWCS(self.acs_file, ext=1)
-        w1z = HSTWCS(self.acs_file, ext=1, wcskey='Z')
+        w1 = wcsutil.HSTWCS(self.acs_file, ext=1)
+        w1z = wcsutil.HSTWCS(self.acs_file, ext=1, wcskey='Z')
         compare_wcs(w1, w1z)
 
     def test_restore_wcs(self):
         # test restore on a file
         altwcs.restoreWCS(self.acs_file, ext=1, wcskey='O')
-        w1o = HSTWCS(self.acs_file, ext=1, wcskey='O')
-        w1 = HSTWCS(self.acs_file, ext=1)
+        w1o = wcsutil.HSTWCS(self.acs_file, ext=1, wcskey='O')
+        w1 = wcsutil.HSTWCS(self.acs_file, ext=1)
         compare_wcs(w1, w1o, exclude_keywords=['ctype'])
 
     def test_restore_wcs_mem(self):
@@ -99,8 +102,8 @@ class TestAltWCS(object):
         f = pyfits.open(self.acs_file, mode='update')
         altwcs.restoreWCS(f, ext=1, wcskey='T')
         f.close()
-        w1o = HSTWCS(self.acs_file, ext=1, wcskey='T')
-        w1 = HSTWCS(self.acs_file, ext=1)
+        w1o = wcsutil.HSTWCS(self.acs_file, ext=1, wcskey='T')
+        w1 = wcsutil.HSTWCS(self.acs_file, ext=1)
         compare_wcs(w1, w1o)
 
     def test_restore_simple(self):
@@ -108,8 +111,8 @@ class TestAltWCS(object):
         altwcs.archiveWCS(self.simplefits, ext=0, wcskey='R')
         pyfits.setval(self.simplefits, ext=0, keyword='CRVAL1R', value=1)
         altwcs.restoreWCS(self.simplefits, ext=0, wcskey='R')
-        wo = HSTWCS(self.simplefits, ext=0, wcskey='R')
-        ws = HSTWCS(self.simplefits, ext=0)
+        wo = wcsutil.HSTWCS(self.simplefits, ext=0, wcskey='R')
+        ws = wcsutil.HSTWCS(self.simplefits, ext=0)
         compare_wcs(ws, wo)
 
     def test_restore_wcs_from_to(self):
@@ -121,25 +124,27 @@ class TestAltWCS(object):
         altwcs.restore_from_to(f, fromext='SCI', toext=['SCI', 'ERR', 'DQ'],
                                wcskey='T')
         f.close()
-        w1o = HSTWCS(self.acs_file, ext=('SCI', 1), wcskey='T')
-        w1 = HSTWCS(self.acs_file, ext=('SCI', 1))
+        w1o = wcsutil.HSTWCS(self.acs_file, ext=('SCI', 1), wcskey='T')
+        w1 = wcsutil.HSTWCS(self.acs_file, ext=('SCI', 1))
         compare_wcs(w1, w1o)
-        w2 = HSTWCS(self.acs_file, ext=('ERR', 1))
+        w2 = wcsutil.HSTWCS(self.acs_file, ext=('ERR', 1))
         compare_wcs(w2, w1o, exclude_keywords=['ctype'])
-        w3 = HSTWCS(self.acs_file, ext=('DQ', 1))
+        w3 = wcsutil.HSTWCS(self.acs_file, ext=('DQ', 1))
         compare_wcs(w3, w1o, exclude_keywords=['ctype'])
-        w4o = HSTWCS(self.acs_file, ext=4, wcskey='T')
-        w4 = HSTWCS(self.acs_file, ext=('SCI', 2))
+        w4o = wcsutil.HSTWCS(self.acs_file, ext=4, wcskey='T')
+        w4 = wcsutil.HSTWCS(self.acs_file, ext=('SCI', 2))
         compare_wcs(w4, w4o)
-        w5 = HSTWCS(self.acs_file, ext=('ERR', 2))
+        w5 = wcsutil.HSTWCS(self.acs_file, ext=('ERR', 2))
         compare_wcs(w5, w4o, exclude_keywords=['ctype'])
-        w6 = HSTWCS(self.acs_file, ext=('DQ', 2))
+        w6 = wcsutil.HSTWCS(self.acs_file, ext=('DQ', 2))
         compare_wcs(w3, w1o, exclude_keywords=['ctype'])
 
     def test_delete_wcs(self):
         #altwcs.archiveWCS(self.acs_file, ext=1, wcskey='Z')
         altwcs.deleteWCS(self.acs_file, ext=1, wcskey='Z')
-        utils.assert_raises(KeyError, HSTWCS, self.acs_file, ext=1, wcskey='Z')
+        #utils.assert_raises(KeyError, wcsutil.HSTWCS, self.acs_file, ext=1, wcskey='Z')
+        with pytest.raises(KeyError):
+            wcsutil.HSTWCS(self.acs_file, ext=1, wcskey='Z')
 
     def test_pars_file_mode1(self):
         assert(not altwcs._parpasscheck(self.acs_file, ext=1, wcskey='Z'))
diff --git a/stwcs/tests/test_headerlet.py b/stwcs/tests/test_headerlet.py
index 48fb470..f4fa050 100644
--- a/stwcs/tests/test_headerlet.py
+++ b/stwcs/tests/test_headerlet.py
@@ -1,9 +1,11 @@
+from __future__ import absolute_import, division, print_function
+
 import shutil
 import os
 from astropy.io import fits
-from stwcs import updatewcs
-from stwcs.wcsutil import headerlet, wcsdiff
-from stwcs.wcsutil import HSTWCS
+from .. import updatewcs
+from ..wcsutil import headerlet, wcsdiff
+from ..wcsutil import HSTWCS
 import numpy as np
 from numpy.testing import utils
 from nose.tools import *
diff --git a/stwcs/tests/test_updatewcs.py b/stwcs/tests/test_updatewcs.py
index dc5a34f..b7e75c8 100644
--- a/stwcs/tests/test_updatewcs.py
+++ b/stwcs/tests/test_updatewcs.py
@@ -1,12 +1,14 @@
+from __future__ import absolute_import, division, print_function
+
 import shutil
 import os
 
 from astropy import wcs
 from astropy.io import fits
-from stwcs import updatewcs
-from stwcs.updatewcs import apply_corrections
-from stwcs.distortion import utils as dutils
-from stwcs.wcsutil import HSTWCS
+from .. import updatewcs
+from ..updatewcs import apply_corrections
+from ..distortion import utils as dutils
+from ..wcsutil import HSTWCS
 import numpy as np
 from numpy.testing import utils
 import pytest
@@ -111,7 +113,7 @@ class TestStwcs(object):
 
         #print('outwcs.wcs.crval = {0}'.format(outwcs.wcs.crval))
         utils.assert_allclose(
-            outwcs.wcs.crval, np.array([5.65109952, -72.0674181]), rtol=1e-7)
+            outwcs.wcs.crval, np.array([5.65109952, -72.0674181]), atol=1e-7)
 
         utils.assert_almost_equal(outwcs.wcs.crpix, np.array([2107.0, 2118.5]))
         utils.assert_almost_equal(
diff --git a/stwcs/updatewcs/__init__.py b/stwcs/updatewcs/__init__.py
index eb5e850..a59f106 100644
--- a/stwcs/updatewcs/__init__.py
+++ b/stwcs/updatewcs/__init__.py
@@ -1,14 +1,16 @@
-from __future__ import absolute_import, division, print_function # confidence high
+from __future__ import absolute_import, division, print_function
 
+import atexit
 from astropy.io import fits
-from stwcs import wcsutil
-from stwcs.wcsutil import HSTWCS
-import stwcs
+from .. import wcsutil
+#from ..wcsutil.hwstwcs import HSTWCS
+
+from .. import __version__
 
 from astropy import wcs as pywcs
 import astropy
 
-from . import utils, corrections, makewcs
+from . import utils, corrections
 from . import npol, det2im
 from stsci.tools import parseinput, fileutil
 from . import apply_corrections
@@ -17,10 +19,10 @@ import time
 import logging
 logger = logging.getLogger('stwcs.updatewcs')
 
-import atexit
 atexit.register(logging.shutdown)
 
-#Note: The order of corrections is important
+# Note: The order of corrections is important
+
 
 def updatewcs(input, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True,
               checkfiles=True, verbose=False):
@@ -62,7 +64,7 @@ def updatewcs(input, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True,
               geis and waiver fits files will be converted to MEF format.
               Default value is True for standalone mode.
     """
-    if verbose == False:
+    if not verbose:
         logger.setLevel(100)
     else:
         formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
@@ -74,12 +76,12 @@ def updatewcs(input, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True,
         logger.setLevel(verbose)
     args = "vacorr=%s, tddcorr=%s, npolcorr=%s, d2imcorr=%s, checkfiles=%s, \
     " % (str(vacorr), str(tddcorr), str(npolcorr),
-                                          str(d2imcorr), str(checkfiles))
+         str(d2imcorr), str(checkfiles))
     logger.info('\n\tStarting UPDATEWCS: %s', time.asctime())
 
     files = parseinput.parseinput(input)[0]
     logger.info("\n\tInput files: %s, " % [i for i in files])
-    logger.info("\n\tInput arguments: %s" %args)
+    logger.info("\n\tInput arguments: %s" % args)
     if checkfiles:
         files = checkFiles(files)
         if not files:
@@ -87,8 +89,8 @@ def updatewcs(input, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True,
             return
 
     for f in files:
-        acorr = apply_corrections.setCorrections(f, vacorr=vacorr, \
-            tddcorr=tddcorr,npolcorr=npolcorr, d2imcorr=d2imcorr)
+        acorr = apply_corrections.setCorrections(f, vacorr=vacorr, tddcorr=tddcorr,
+                                                 npolcorr=npolcorr, d2imcorr=d2imcorr)
         if 'MakeWCS' in acorr and newIDCTAB(f):
             logger.warning("\n\tNew IDCTAB file detected. All current WCSs will be deleted")
             cleanWCS(f)
@@ -97,6 +99,7 @@ def updatewcs(input, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True,
 
     return files
 
+
 def makecorr(fname, allowed_corr):
     """
     Purpose
@@ -111,11 +114,11 @@ def makecorr(fname, allowed_corr):
     """
     logger.info("Allowed corrections: {0}".format(allowed_corr))
     f = fits.open(fname, mode='update')
-    #Determine the reference chip and create the reference HSTWCS object
+    # Determine the reference chip and create the reference HSTWCS object
     nrefchip, nrefext = getNrefchip(f)
     wcsutil.restoreWCS(f, nrefext, wcskey='O')
-    rwcs = HSTWCS(fobj=f, ext=nrefext)
-    rwcs.readModel(update=True,header=f[nrefext].header)
+    rwcs = wcsutil.HSTWCS(fobj=f, ext=nrefext)
+    rwcs.readModel(update=True, header=f[nrefext].header)
 
     if 'DET2IMCorr' in allowed_corr:
         kw2update = det2im.DET2IMCorr.updateWCS(f)
@@ -127,16 +130,16 @@ def makecorr(fname, allowed_corr):
 
         if 'extname' in extn.header:
             extname = extn.header['extname'].lower()
-            if  extname == 'sci':
+            if extname == 'sci':
                 wcsutil.restoreWCS(f, ext=i, wcskey='O')
                 sciextver = extn.header['extver']
                 ref_wcs = rwcs.deepcopy()
                 hdr = extn.header
-                ext_wcs = HSTWCS(fobj=f, ext=i)
-                ### check if it exists first!!!
+                ext_wcs = wcsutil.HSTWCS(fobj=f, ext=i)
+                # check if it exists first!!!
                 # 'O ' can be safely archived again because it has been restored first.
                 wcsutil.archiveWCS(f, ext=i, wcskey="O", wcsname="OPUS", reusekey=True)
-                ext_wcs.readModel(update=True,header=hdr)
+                ext_wcs.readModel(update=True, header=hdr)
                 for c in allowed_corr:
                     if c != 'NPOLCorr' and c != 'DET2IMCorr':
                         corr_klass = corrections.__getattribute__(c)
@@ -147,14 +150,14 @@ def makecorr(fname, allowed_corr):
                 idcname = f[0].header.get('IDCTAB', " ")
                 if idcname.strip() and 'idc.fits' in idcname:
                     wname = ''.join(['IDC_',
-                                utils.extract_rootname(idcname,suffix='_idc')])
+                                     utils.extract_rootname(idcname, suffix='_idc')])
                 else: wname = " "
                 hdr['WCSNAME'] = wname
 
             elif extname in ['err', 'dq', 'sdq', 'samp', 'time']:
                 cextver = extn.header['extver']
                 if cextver == sciextver:
-                    hdr = f[('SCI',sciextver)].header
+                    hdr = f[('SCI', sciextver)].header
                     w = pywcs.WCS(hdr, f)
                     copyWCS(w, extn.header)
 
@@ -167,14 +170,14 @@ def makecorr(fname, allowed_corr):
             f[1].header[kw] = kw2update[kw]
     # Finally record the version of the software which updated the WCS
     if 'HISTORY' in f[0].header:
-        f[0].header.set('UPWCSVER', value=stwcs.__version__,
+        f[0].header.set('UPWCSVER', value=__version__,
                         comment="Version of STWCS used to updated the WCS",
                         before='HISTORY')
         f[0].header.set('PYWCSVER', value=astropy.__version__,
                         comment="Version of PYWCS used to updated the WCS",
                         before='HISTORY')
     elif 'ASN_MTYP' in f[0].header:
-        f[0].header.set('UPWCSVER', value=stwcs.__version__,
+        f[0].header.set('UPWCSVER', value=__version__,
                         comment="Version of STWCS used to updated the WCS",
                         after='ASN_MTYP')
         f[0].header.set('PYWCSVER', value=astropy.__version__,
@@ -185,20 +188,21 @@ def makecorr(fname, allowed_corr):
         for i in range(len(f[0].header) - 1, 0, -1):
             if f[0].header[i].strip() != '':
                 break
-            f[0].header.set('UPWCSVER', stwcs.__version__,
+            f[0].header.set('UPWCSVER', __version__,
                             "Version of STWCS used to updated the WCS",
                             after=i)
             f[0].header.set('PYWCSVER', astropy.__version__,
                             "Version of PYWCS used to updated the WCS",
                             after=i)
     # add additional keywords to be used by headerlets
-    distdict = utils.construct_distname(f,rwcs)
+    distdict = utils.construct_distname(f, rwcs)
     f[0].header['DISTNAME'] = distdict['DISTNAME']
     f[0].header['SIPNAME'] = distdict['SIPNAME']
     # Make sure NEXTEND keyword remains accurate
-    f[0].header['NEXTEND'] = len(f)-1
+    f[0].header['NEXTEND'] = len(f) - 1
     f.close()
 
+
 def copyWCS(w, ehdr):
     """
     This is a convenience function to copy a WCS object
@@ -214,6 +218,7 @@ def copyWCS(w, ehdr):
         key = k[:7]
         ehdr[key] = hwcs[k]
 
+
 def getNrefchip(fobj):
     """
 
@@ -235,15 +240,15 @@ def getNrefchip(fobj):
 
     if instrument == 'WFPC2':
         chipkw = 'DETECTOR'
-        extvers = [("SCI",img.header['EXTVER']) for img in
-                   fobj[1:] if img.header['EXTNAME'].lower()=='sci']
+        extvers = [("SCI", img.header['EXTVER']) for img in
+                   fobj[1:] if img.header['EXTNAME'].lower() == 'sci']
         detectors = [img.header[chipkw] for img in fobj[1:] if
-                     img.header['EXTNAME'].lower()=='sci']
+                     img.header['EXTNAME'].lower() == 'sci']
         fitsext = [i for i in range(len(fobj))[1:] if
-                   fobj[i].header['EXTNAME'].lower()=='sci']
-        det2ext=dict(list(zip(detectors, extvers)))
-        ext2det=dict(list(zip(extvers, detectors)))
-        ext2fitsext=dict(list(zip(extvers, fitsext)))
+                   fobj[i].header['EXTNAME'].lower() == 'sci']
+        det2ext = dict(list(zip(detectors, extvers)))
+        ext2det = dict(list(zip(extvers, detectors)))
+        ext2fitsext = dict(list(zip(extvers, fitsext)))
 
         if 3 not in detectors:
             nrefchip = ext2det.pop(extvers[0])
@@ -256,15 +261,15 @@ def getNrefchip(fobj):
     elif (instrument == 'ACS' and fobj[0].header['DETECTOR'] == 'WFC') or \
          (instrument == 'WFC3' and fobj[0].header['DETECTOR'] == 'UVIS'):
         chipkw = 'CCDCHIP'
-        extvers = [("SCI",img.header['EXTVER']) for img in
-                   fobj[1:] if img.header['EXTNAME'].lower()=='sci']
+        extvers = [("SCI", img.header['EXTVER']) for img in
+                   fobj[1:] if img.header['EXTNAME'].lower() == 'sci']
         detectors = [img.header[chipkw] for img in fobj[1:] if
-                     img.header['EXTNAME'].lower()=='sci']
+                     img.header['EXTNAME'].lower() == 'sci']
         fitsext = [i for i in range(len(fobj))[1:] if
-                   fobj[i].header['EXTNAME'].lower()=='sci']
-        det2ext=dict(list(zip(detectors, extvers)))
-        ext2det=dict(list(zip(extvers, detectors)))
-        ext2fitsext=dict(list(zip(extvers, fitsext)))
+                   fobj[i].header['EXTNAME'].lower() == 'sci']
+        det2ext = dict(list(zip(detectors, extvers)))
+        ext2det = dict(list(zip(extvers, detectors)))
+        ext2fitsext = dict(list(zip(extvers, fitsext)))
 
         if 2 not in detectors:
             nrefchip = ext2det.pop(extvers[0])
@@ -276,12 +281,13 @@ def getNrefchip(fobj):
     else:
         for i in range(len(fobj)):
             extname = fobj[i].header.get('EXTNAME', None)
-            if extname != None and extname.lower == 'sci':
+            if extname is not None and extname.lower == 'sci':
                 nrefext = i
                 break
 
     return nrefchip, nrefext
 
+
 def checkFiles(input):
     """
     Checks that input files are in the correct format.
@@ -292,13 +298,14 @@ def checkFiles(input):
     removed_files = []
     newfiles = []
     if not isinstance(input, list):
-        input=[input]
+        input = [input]
 
     for file in input:
         try:
-                imgfits,imgtype = fileutil.isFits(file)
+                imgfits, imgtype = fileutil.isFits(file)
         except IOError:
-            logger.warning( "\n\tFile %s could not be found, removing it from the input list.\n" %file)
+            logger.warning("File {0} could not be found, removing it from the"
+                           "input list.".format(file))
             removed_files.append(file)
             continue
         # Check for existence of waiver FITS input, and quit if found.
@@ -306,8 +313,9 @@ def checkFiles(input):
         if imgfits:
             if imgtype == 'waiver':
                 newfilename = waiver2mef(file, convert_dq=True)
-                if newfilename == None:
-                    logger.warning("\n\tRemoving file %s from input list - could not convert waiver to mef" %file)
+                if newfilename is None:
+                    logger.warning("Could not convert waiver to mef."
+                                   "Removing file {0} from input list".format(file))
                     removed_files.append(file)
                 else:
                     newfiles.append(newfilename)
@@ -319,24 +327,26 @@ def checkFiles(input):
         # Convert the corresponding data quality file if present
         if not imgfits:
             newfilename = geis2mef(file, convert_dq=True)
-            if newfilename == None:
-                logger.warning("\n\tRemoving file %s from input list - could not convert geis to mef" %file)
+            if newfilename is None:
+                logger.warning("Could not convert file {0} from geis to mef, removing it from input list".format(file))
                 removed_files.append(file)
             else:
                 newfiles.append(newfilename)
     if removed_files:
-        logger.warning('\n\tThe following files will be removed from the list of files to be processed %s' % removed_files)
+        logger.warning('\n\tThe following files will be removed from the list of files',
+                       'to be processed %s' % removed_files)
 
     newfiles = checkFiles(newfiles)[0]
     logger.info("\n\tThese files passed the input check and will be processed: %s" % newfiles)
     return newfiles
 
+
 def newIDCTAB(fname):
-    #When this is called we know there's a kw IDCTAB in the header
+    # When this is called we know there's a kw IDCTAB in the header
     hdul = fits.open(fname)
     idctab = fileutil.osfn(hdul[0].header['IDCTAB'])
     try:
-        #check for the presence of IDCTAB in the first extension
+        # check for the presence of IDCTAB in the first extension
         oldidctab = fileutil.osfn(hdul[1].header['IDCTAB'])
     except KeyError:
         return False
@@ -345,6 +355,7 @@ def newIDCTAB(fname):
     else:
         return True
 
+
 def cleanWCS(fname):
     # A new IDCTAB means all previously computed WCS's are invalid
     # We are deleting all of them except the original OPUS WCS.
@@ -363,6 +374,7 @@ def cleanWCS(fname):
             # Some extensions don't have the alternate (or any) WCS keywords
             continue
 
+
 def getCorrections(instrument):
     """
     Print corrections available for an instrument
@@ -373,4 +385,4 @@ def getCorrections(instrument):
     acorr = apply_corrections.allowed_corrections[instrument]
 
     print("The following corrections will be performed for instrument %s\n" % instrument)
-    for c in acorr: print(c,': ' ,  apply_corrections.cnames[c])
+    for c in acorr: print(c, ': ', apply_corrections.cnames[c])
diff --git a/stwcs/updatewcs/apply_corrections.py b/stwcs/updatewcs/apply_corrections.py
index 86b623a..4a8e5ac 100644
--- a/stwcs/updatewcs/apply_corrections.py
+++ b/stwcs/updatewcs/apply_corrections.py
@@ -1,37 +1,35 @@
-from __future__ import division, print_function  # confidence high
+from __future__ import absolute_import, division, print_function
 
-import os
+import os.path
 from astropy.io import fits
-import time
 from stsci.tools import fileutil
-import os.path
-from stwcs.wcsutil import altwcs
 from . import utils
 from . import wfpc2_dgeo
 
 import logging
 logger = logging.getLogger("stwcs.updatewcs.apply_corrections")
 
-#Note: The order of corrections is important
+# Note: The order of corrections is important
 
 
 # A dictionary which lists the allowed corrections for each instrument.
 # These are the default corrections applied also in the pipeline.
 
-allowed_corrections={'WFPC2': ['DET2IMCorr', 'MakeWCS','CompSIP', 'VACorr'],
-                    'ACS': ['DET2IMCorr', 'TDDCorr', 'MakeWCS', 'CompSIP','VACorr', 'NPOLCorr'],
-                    'STIS': ['MakeWCS', 'CompSIP','VACorr'],
-                    'NICMOS': ['MakeWCS', 'CompSIP','VACorr'],
-                    'WFC3': ['DET2IMCorr', 'MakeWCS', 'CompSIP','VACorr', 'NPOLCorr'],
-                    }
+allowed_corrections = {'WFPC2': ['DET2IMCorr', 'MakeWCS', 'CompSIP', 'VACorr'],
+                       'ACS': ['DET2IMCorr', 'TDDCorr', 'MakeWCS', 'CompSIP', 'VACorr', 'NPOLCorr'],
+                       'STIS': ['MakeWCS', 'CompSIP', 'VACorr'],
+                       'NICMOS': ['MakeWCS', 'CompSIP', 'VACorr'],
+                       'WFC3': ['DET2IMCorr', 'MakeWCS', 'CompSIP', 'VACorr', 'NPOLCorr'],
+                       }
 
 cnames = {'DET2IMCorr': 'Detector to Image Correction',
-         'TDDCorr': 'Time Dependent Distortion Correction',
-         'MakeWCS': 'Recalculate basic WCS keywords based on the distortion model',
-         'CompSIP': 'Given IDCTAB distortion model calculate the SIP coefficients',
-         'VACorr':  'Velocity Aberration Correction',
-         'NPOLCorr': 'Lookup Table Distortion'
-         }
+          'TDDCorr': 'Time Dependent Distortion Correction',
+          'MakeWCS': 'Recalculate basic WCS keywords based on the distortion model',
+          'CompSIP': 'Given IDCTAB distortion model calculate the SIP coefficients',
+          'VACorr': 'Velocity Aberration Correction',
+          'NPOLCorr': 'Lookup Table Distortion'
+          }
+
 
 def setCorrections(fname, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=True):
     """
@@ -40,7 +38,7 @@ def setCorrections(fname, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=Tru
     for the instrument.
     """
     instrument = fits.getval(fname, 'INSTRUME')
-    # make a copy of this list !
+    # make a copy of this list
     acorr = allowed_corrections[instrument][:]
 
     # For WFPC2 images, the old-style DGEOFILE needs to be
@@ -56,18 +54,22 @@ def setCorrections(fname, vacorr=True, tddcorr=True, npolcorr=True, d2imcorr=Tru
         if 'MakeWCS' in acorr: acorr.remove('MakeWCS')
         if 'CompSIP' in acorr: acorr.remove('CompSIP')
 
-    if 'VACorr' in acorr and vacorr==False:  acorr.remove('VACorr')
+    if 'VACorr' in acorr and not vacorr:
+        acorr.remove('VACorr')
     if 'TDDCorr' in acorr:
         tddcorr = applyTDDCorr(fname, tddcorr)
-        if tddcorr == False: acorr.remove('TDDCorr')
+        if not tddcorr:
+            acorr.remove('TDDCorr')
 
     if 'NPOLCorr' in acorr:
         npolcorr = applyNpolCorr(fname, npolcorr)
-        if npolcorr == False: acorr.remove('NPOLCorr')
+        if not npolcorr:
+            acorr.remove('NPOLCorr')
     if 'DET2IMCorr' in acorr:
         d2imcorr = applyD2ImCorr(fname, d2imcorr)
-        if d2imcorr == False: acorr.remove('DET2IMCorr')
-    logger.info("\n\tCorrections to be applied to %s: %s " % (fname, str(acorr)))
+        if not d2imcorr:
+            acorr.remove('DET2IMCorr')
+    logger.info("Corrections to be applied to {0} {1}".format(fname, acorr))
     return acorr
 
 
@@ -119,22 +121,21 @@ def applyTDDCorr(fname, utddcorr):
     except KeyError:
         tddswitch = 'PERFORM'
 
-    if instrument == 'ACS' and detector == 'WFC' and utddcorr == True and tddswitch == 'PERFORM':
+    if instrument == 'ACS' and detector == 'WFC' and utddcorr and tddswitch == 'PERFORM':
         tddcorr = True
         try:
             idctab = phdr['IDCTAB']
         except KeyError:
             tddcorr = False
-            #print "***IDCTAB keyword not found - not applying TDD correction***\n"
         if os.path.exists(fileutil.osfn(idctab)):
             tddcorr = True
         else:
             tddcorr = False
-            #print "***IDCTAB file not found - not applying TDD correction***\n"
     else:
         tddcorr = False
     return tddcorr
 
+
 def applyNpolCorr(fname, unpolcorr):
     """
     Determines whether non-polynomial distortion lookup tables should be added
@@ -156,9 +157,8 @@ def applyNpolCorr(fname, unpolcorr):
             return False
         fnpol0 = fileutil.osfn(fnpol0)
         if not fileutil.findFile(fnpol0):
-            msg =  """\n\tKw "NPOLFILE" exists in primary header but file %s not found
-                      Non-polynomial distortion correction will not be applied\n
-                    """ % fnpol0
+            msg = '"NPOLFILE" exists in primary header but file {0} not found.'
+            'Non-polynomial distortion correction will not be applied.'.format(file)
             logger.critical(msg)
             raise IOError("NPOLFILE {0} not found".format(fnpol0))
         try:
@@ -176,7 +176,7 @@ def applyNpolCorr(fname, unpolcorr):
             else:
                 # npl file defined in first extension may not be found
                 # but if a valid kw exists in the primary header, non-polynomial
-                #distortion correction should be applied.
+                # distortion correction should be applied.
                 applyNPOLCorr = True
         except KeyError:
             # the case of "NPOLFILE" kw present in primary header but "NPOLEXT" missing
@@ -191,6 +191,7 @@ def applyNpolCorr(fname, unpolcorr):
             applyNPOLCorr = False
     return (applyNPOLCorr and unpolcorr)
 
+
 def isOldStyleDGEO(fname, dgname):
     # checks if the file defined in a NPOLFILE kw is a full size
     # (old style) image
@@ -209,6 +210,7 @@ def isOldStyleDGEO(fname, dgname):
     else:
         return False
 
+
 def applyD2ImCorr(fname, d2imcorr):
     applyD2IMCorr = True
     try:
diff --git a/stwcs/updatewcs/corrections.py b/stwcs/updatewcs/corrections.py
index d3641eb..975a806 100644
--- a/stwcs/updatewcs/corrections.py
+++ b/stwcs/updatewcs/corrections.py
@@ -1,8 +1,9 @@
-from __future__ import division, print_function # confidence high
+from __future__ import absolute_import, division, print_function
 
 import copy
 import datetime
-import logging, time
+import logging
+import time
 import numpy as np
 from numpy import linalg
 from stsci.tools import fileutil
@@ -11,11 +12,12 @@ from . import npol
 from . import makewcs
 from .utils import diff_angles
 
-logger=logging.getLogger('stwcs.updatewcs.corrections')
+logger = logging.getLogger('stwcs.updatewcs.corrections')
 
 MakeWCS = makewcs.MakeWCS
 NPOLCorr = npol.NPOLCorr
 
+
 class TDDCorr(object):
     """
     Apply time dependent distortion correction to distortion coefficients and basic
@@ -70,39 +72,39 @@ class TDDCorr(object):
         ext_wcs.idcmodel.ocx = copy.deepcopy(ext_wcs.idcmodel.cx)
         ext_wcs.idcmodel.ocy = copy.deepcopy(ext_wcs.idcmodel.cy)
 
-        newkw = {'TDDALPHA': None, 'TDDBETA':None,
-                'OCX10':ext_wcs.idcmodel.ocx[1,0],
-                'OCX11':ext_wcs.idcmodel.ocx[1,1],
-                'OCY10':ext_wcs.idcmodel.ocy[1,0],
-                'OCY11':ext_wcs.idcmodel.ocy[1,1],
-                'TDD_CTA':None, 'TDD_CTB':None,
-                'TDD_CYA':None, 'TDD_CYB':None,
-                'TDD_CXA':None, 'TDD_CXB':None}
-
-        if ext_wcs.idcmodel.refpix['skew_coeffs']is not None and \
-            ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTB'] is not None:
+        newkw = {'TDDALPHA': None, 'TDDBETA': None,
+                 'OCX10': ext_wcs.idcmodel.ocx[1, 0],
+                 'OCX11': ext_wcs.idcmodel.ocx[1, 1],
+                 'OCY10': ext_wcs.idcmodel.ocy[1, 0],
+                 'OCY11': ext_wcs.idcmodel.ocy[1, 1],
+                 'TDD_CTA': None, 'TDD_CTB': None,
+                 'TDD_CYA': None, 'TDD_CYB': None,
+                 'TDD_CXA': None, 'TDD_CXB': None
+                 }
+
+        if ext_wcs.idcmodel.refpix['skew_coeffs'] is not None and \
+                ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTB'] is not None:
             cls.apply_tdd2idc2015(ref_wcs)
             cls.apply_tdd2idc2015(ext_wcs)
 
-            newkw.update({
-                    'TDD_CTA':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTA'],
-                    'TDD_CYA':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CYA'],
-                    'TDD_CXA':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CXA'],
-                    'TDD_CTB':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTB'],
-                    'TDD_CYB':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CYB'],
-                    'TDD_CXB':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CXB']})
-
-        elif ext_wcs.idcmodel.refpix['skew_coeffs']is not None and \
-            ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_BETA'] is not None:
-            logger.info("\n\t Applying 2014-calibrated TDD: %s" % time.asctime())
+            newkw.update({'TDD_CTA': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTA'],
+                          'TDD_CYA': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CYA'],
+                          'TDD_CXA': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CXA'],
+                          'TDD_CTB': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CTB'],
+                          'TDD_CYB': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CYB'],
+                          'TDD_CXB': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CXB']
+                          })
+
+        elif ext_wcs.idcmodel.refpix['skew_coeffs'] is not None and \
+                ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_BETA'] is not None:
+            logger.info("Applying 2014-calibrated TDD: {0}".format(time.asctime()))
             # We have 2014-calibrated TDD, not J.A.-style TDD
             cls.apply_tdd2idc2(ref_wcs)
             cls.apply_tdd2idc2(ext_wcs)
-            newkw.update({'TDD_CYA':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_ALPHA'],
-                    'TDD_CYB':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_BETA'],
-                    'TDD_CXA':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CX_ALPHA'],
-                    'TDD_CXB':ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CX_BETA']})
-
+            newkw.update({'TDD_CYA': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_ALPHA'],
+                          'TDD_CYB': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CY_BETA'],
+                          'TDD_CXA': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CX_ALPHA'],
+                          'TDD_CXB': ext_wcs.idcmodel.refpix['skew_coeffs']['TDD_CX_BETA']})
         else:
             alpha, beta = cls.compute_alpha_beta(ext_wcs)
             cls.apply_tdd2idc(ref_wcs, alpha, beta)
@@ -111,8 +113,7 @@ class TDDCorr(object):
             ext_wcs.idcmodel.refpix['TDDBETA'] = beta
             ref_wcs.idcmodel.refpix['TDDALPHA'] = alpha
             ref_wcs.idcmodel.refpix['TDDBETA'] = beta
-
-            newkw.update( {'TDDALPHA': alpha, 'TDDBETA':beta} )
+            newkw.update({'TDDALPHA': alpha, 'TDDBETA': beta} )
 
         return newkw
     updateWCS = classmethod(updateWCS)
@@ -121,10 +122,10 @@ class TDDCorr(object):
         """ Applies 2015-calibrated TDD correction to a couple of IDCTAB
             coefficients for ACS/WFC observations.
         """
-        if not isinstance(hwcs.date_obs,float):
-            year,month,day = hwcs.date_obs.split('-')
-            rdate = datetime.datetime(int(year),int(month),int(day))
-            rday = float(rdate.strftime("%j"))/365.25 + rdate.year
+        if not isinstance(hwcs.date_obs, float):
+            year, month, day = hwcs.date_obs.split('-')
+            rdate = datetime.datetime(int(year), int(month), int(day))
+            rday = float(rdate.strftime("%j")) / 365.25 + rdate.year
         else:
             rday = hwcs.date_obs
 
@@ -132,12 +133,11 @@ class TDDCorr(object):
         delta_date = rday - skew_coeffs['TDD_DATE']
 
         if skew_coeffs['TDD_CXB'] is not None:
-            hwcs.idcmodel.cx[1,1] +=  skew_coeffs['TDD_CXB']*delta_date
+            hwcs.idcmodel.cx[1, 1] += skew_coeffs['TDD_CXB'] * delta_date
         if skew_coeffs['TDD_CTB'] is not None:
-            hwcs.idcmodel.cy[1,1] += skew_coeffs['TDD_CTB']*delta_date
+            hwcs.idcmodel.cy[1, 1] += skew_coeffs['TDD_CTB'] * delta_date
         if skew_coeffs['TDD_CYB'] is not None:
-            hwcs.idcmodel.cy[1,0] +=  skew_coeffs['TDD_CYB']*delta_date
-        #print("CX[1,1]_TDD={},  CY[1,1]_TDD={},  CY[1,0]_TDD={}".format(hwcs.idcmodel.cx[1,1],hwcs.idcmodel.cy[1,1],hwcs.idcmodel.cy[1,0]))
+            hwcs.idcmodel.cy[1, 0] += skew_coeffs['TDD_CYB'] * delta_date
 
     apply_tdd2idc2015 = classmethod(apply_tdd2idc2015)
 
@@ -145,10 +145,10 @@ class TDDCorr(object):
         """ Applies 2014-calibrated TDD correction to single IDCTAB coefficient
             of an ACS/WFC observation.
         """
-        if not isinstance(hwcs.date_obs,float):
-            year,month,day = hwcs.date_obs.split('-')
-            rdate = datetime.datetime(int(year),int(month),int(day))
-            rday = float(rdate.strftime("%j"))/365.25 + rdate.year
+        if not isinstance(hwcs.date_obs, float):
+            year, month, day = hwcs.date_obs.split('-')
+            rdate = datetime.datetime(int(year), int(month), int(day))
+            rday = float(rdate.strftime("%j")) / 365.25 + rdate.year
         else:
             rday = hwcs.date_obs
 
@@ -156,21 +156,24 @@ class TDDCorr(object):
         cy_beta = skew_coeffs['TDD_CY_BETA']
         cy_alpha = skew_coeffs['TDD_CY_ALPHA']
         delta_date = rday - skew_coeffs['TDD_DATE']
-        print("DELTA_DATE: {0}   based on rday: {1}, TDD_DATE: {2}".format(delta_date,rday,skew_coeffs['TDD_DATE']))
+        logger.info("DELTA_DATE: {0} based on rday: {1}, TDD_DATE: {2}".format(delta_date, rday,
+                                                                               skew_coeffs['TDD_DATE']))
 
         if cy_alpha is None:
-            hwcs.idcmodel.cy[1,1] += cy_beta*delta_date
+            hwcs.idcmodel.cy[1, 1] += cy_beta * delta_date
         else:
-            new_beta = cy_alpha + cy_beta*delta_date
-            hwcs.idcmodel.cy[1,1] = new_beta
-        print("CY11: {0} based on alpha: {1}, beta: {2}".format(hwcs.idcmodel.cy[1,1],cy_alpha,cy_beta))
-
+            new_beta = cy_alpha + cy_beta * delta_date
+            hwcs.idcmodel.cy[1, 1] = new_beta
+        logger.info("CY11: {0} based on alpha: {1}, beta: {2}".format(hwcs.idcmodel.cy[1, 1],
+                                                                      cy_alpha, cy_beta))
+        
         cx_beta = skew_coeffs['TDD_CX_BETA']
         cx_alpha = skew_coeffs['TDD_CX_ALPHA']
         if cx_alpha is not None:
-            new_beta = cx_alpha + cx_beta*delta_date
-            hwcs.idcmodel.cx[1,1] = new_beta
-            print("CX11: {0} based on alpha: {1}, beta: {2}".format(new_beta,cx_alpha,cx_beta))
+            new_beta = cx_alpha + cx_beta * delta_date
+            hwcs.idcmodel.cx[1, 1] = new_beta
+            logger.info("CX11: {0} based on alpha: {1}, beta: {2}".format(new_beta,
+                                                                          cx_alpha, cx_beta))
 
     apply_tdd2idc2 = classmethod(apply_tdd2idc2)
 
@@ -182,11 +185,12 @@ class TDDCorr(object):
         theta_v2v3 = 2.234529
         mrotp = fileutil.buildRotMatrix(theta_v2v3)
         mrotn = fileutil.buildRotMatrix(-theta_v2v3)
-        tdd_mat = np.array([[1+(beta/2048.), alpha/2048.],[alpha/2048.,1-(beta/2048.)]],np.float64)
+        tdd_mat = np.array([[1 + (beta / 2048.), alpha / 2048.],
+                            [alpha / 2048., 1 - (beta / 2048.)]], np.float64)
         abmat1 = np.dot(tdd_mat, mrotn)
-        abmat2 = np.dot(mrotp,abmat1)
+        abmat2 = np.dot(mrotp, abmat1)
         xshape, yshape = hwcs.idcmodel.cx.shape, hwcs.idcmodel.cy.shape
-        icxy = np.dot(abmat2,[hwcs.idcmodel.cx.ravel(), hwcs.idcmodel.cy.ravel()])
+        icxy = np.dot(abmat2, [hwcs.idcmodel.cx.ravel(), hwcs.idcmodel.cy.ravel()])
         hwcs.idcmodel.cx = icxy[0]
         hwcs.idcmodel.cy = icxy[1]
         hwcs.idcmodel.cx.shape = xshape
@@ -209,10 +213,10 @@ class TDDCorr(object):
         alpha = 0.095 + 0.090*(rday-dday)/2.5
         beta = -0.029 - 0.030*(rday-dday)/2.5
         """
-        if not isinstance(ext_wcs.date_obs,float):
-            year,month,day = ext_wcs.date_obs.split('-')
-            rdate = datetime.datetime(int(year),int(month),int(day))
-            rday = float(rdate.strftime("%j"))/365.25 + rdate.year
+        if not isinstance(ext_wcs.date_obs, float):
+            year, month, day = ext_wcs.date_obs.split('-')
+            rdate = datetime.datetime(int(year), int(month), int(day))
+            rday = float(rdate.strftime("%j")) / 365.25 + rdate.year
         else:
             rday = ext_wcs.date_obs
 
@@ -220,26 +224,27 @@ class TDDCorr(object):
         if skew_coeffs is None:
             # Only print out warning for post-SM4 data where this may matter
             if rday > 2009.0:
-                err_str =  "------------------------------------------------------------------------  \n"
+                err_str = "------------------------------------------------------------------------  \n"
                 err_str += "WARNING: the IDCTAB geometric distortion file specified in the image      \n"
                 err_str += "         header did not have the time-dependent distortion coefficients.  \n"
                 err_str += "         The pre-SM4 time-dependent skew solution will be used by default.\n"
                 err_str += "         Please update IDCTAB with new reference file from HST archive.   \n"
-                err_str +=  "------------------------------------------------------------------------  \n"
+                err_str += "------------------------------------------------------------------------  \n"
                 print(err_str)
             # Using default pre-SM4 coefficients
-            skew_coeffs = {'TDD_A':[0.095,0.090/2.5],
-                        'TDD_B':[-0.029,-0.030/2.5],
-                        'TDD_DATE':2004.5,'TDDORDER':1}
+            skew_coeffs = {'TDD_A': [0.095, 0.090 / 2.5],
+                           'TDD_B': [-0.029, -0.030 / 2.5],
+                           'TDD_DATE': 2004.5,
+                           'TDDORDER': 1}
 
         alpha = 0
         beta = 0
         # Compute skew terms, allowing for non-linear coefficients as well
-        for c in range(skew_coeffs['TDDORDER']+1):
-            alpha += skew_coeffs['TDD_A'][c]* np.power((rday-skew_coeffs['TDD_DATE']),c)
-            beta += skew_coeffs['TDD_B'][c]*np.power((rday-skew_coeffs['TDD_DATE']),c)
+        for c in range(skew_coeffs['TDDORDER'] + 1):
+            alpha += skew_coeffs['TDD_A'][c] * np.power((rday - skew_coeffs['TDD_DATE']), c)
+            beta += skew_coeffs['TDD_B'][c] * np.power((rday - skew_coeffs['TDD_DATE']), c)
 
-        return alpha,beta
+        return alpha, beta
     compute_alpha_beta = classmethod(compute_alpha_beta)
 
 
@@ -254,21 +259,21 @@ class VACorr(object):
 
     """
     def updateWCS(cls, ext_wcs, ref_wcs):
-        logger.info("\n\tStarting VACorr: %s" % time.asctime())
+        logger.info("Starting VACorr: %s" % time.asctime())
         if ext_wcs.vafactor != 1:
             ext_wcs.wcs.cd = ext_wcs.wcs.cd * ext_wcs.vafactor
-            crval0 = ref_wcs.wcs.crval[0] + ext_wcs.vafactor*diff_angles(ext_wcs.wcs.crval[0],
-                                                                         ref_wcs.wcs.crval[0])
-            crval1 = ref_wcs.wcs.crval[1] + ext_wcs.vafactor*diff_angles(ext_wcs.wcs.crval[1],
-                                                                         ref_wcs.wcs.crval[1])
-            crval = np.array([crval0,crval1])
+            crval0 = ref_wcs.wcs.crval[0] + ext_wcs.vafactor * diff_angles(ext_wcs.wcs.crval[0],
+                                                                           ref_wcs.wcs.crval[0])
+            crval1 = ref_wcs.wcs.crval[1] + ext_wcs.vafactor * diff_angles(ext_wcs.wcs.crval[1],
+                                                                           ref_wcs.wcs.crval[1])
+            crval = np.array([crval0, crval1])
             ext_wcs.wcs.crval = crval
             ext_wcs.wcs.set()
         else:
             pass
-        kw2update={'CD1_1': ext_wcs.wcs.cd[0,0], 'CD1_2':ext_wcs.wcs.cd[0,1],
-                    'CD2_1':ext_wcs.wcs.cd[1,0], 'CD2_2':ext_wcs.wcs.cd[1,1],
-                    'CRVAL1':ext_wcs.wcs.crval[0], 'CRVAL2':ext_wcs.wcs.crval[1]}
+        kw2update = {'CD1_1': ext_wcs.wcs.cd[0, 0], 'CD1_2': ext_wcs.wcs.cd[0, 1],
+                     'CD2_1': ext_wcs.wcs.cd[1, 0], 'CD2_2': ext_wcs.wcs.cd[1, 1],
+                     'CRVAL1': ext_wcs.wcs.crval[0], 'CRVAL2': ext_wcs.wcs.crval[1]}
         return kw2update
 
     updateWCS = classmethod(updateWCS)
@@ -291,34 +296,34 @@ class CompSIP(object):
 
     """
     def updateWCS(cls, ext_wcs, ref_wcs):
-        logger.info("\n\tStarting CompSIP: %s" %time.asctime())
+        logger.info("Starting CompSIP: {0}".format(time.asctime()))
         kw2update = {}
         if not ext_wcs.idcmodel:
-            logger.info("IDC model not found, SIP coefficient will not be computed")
+            logger.info("IDC model not found, SIP coefficient will not be computed.")
             return kw2update
         order = ext_wcs.idcmodel.norder
         kw2update['A_ORDER'] = order
         kw2update['B_ORDER'] = order
-        pscale = ext_wcs.idcmodel.refpix['PSCALE']
+        # pscale = ext_wcs.idcmodel.refpix['PSCALE']
 
         cx = ext_wcs.idcmodel.cx
         cy = ext_wcs.idcmodel.cy
 
-        matr = np.array([[cx[1,1],cx[1,0]], [cy[1,1],cy[1,0]]], dtype=np.float64)
+        matr = np.array([[cx[1, 1], cx[1, 0]], [cy[1, 1], cy[1, 0]]], dtype=np.float64)
         imatr = linalg.inv(matr)
-        akeys1 = np.zeros((order+1,order+1), dtype=np.float64)
-        bkeys1 = np.zeros((order+1,order+1), dtype=np.float64)
-        for n in range(order+1):
-            for m in range(order+1):
-                if n >= m and n>=2:
-                    idcval = np.array([[cx[n,m]],[cy[n,m]]])
+        akeys1 = np.zeros((order + 1, order + 1), dtype=np.float64)
+        bkeys1 = np.zeros((order + 1, order + 1), dtype=np.float64)
+        for n in range(order + 1):
+            for m in range(order + 1):
+                if n >= m and n >= 2:
+                    idcval = np.array([[cx[n, m]], [cy[n, m]]])
                     sipval = np.dot(imatr, idcval)
-                    akeys1[m,n-m] = sipval[0]
-                    bkeys1[m,n-m] = sipval[1]
-                    Akey="A_%d_%d" % (m,n-m)
-                    Bkey="B_%d_%d" % (m,n-m)
-                    kw2update[Akey] = sipval[0,0] * ext_wcs.binned
-                    kw2update[Bkey] = sipval[1,0] * ext_wcs.binned
+                    akeys1[m, n - m] = sipval[0]
+                    bkeys1[m, n - m] = sipval[1]
+                    Akey = "A_%d_%d" % (m, n - m)
+                    Bkey = "B_%d_%d" % (m, n - m)
+                    kw2update[Akey] = sipval[0, 0] * ext_wcs.binned
+                    kw2update[Bkey] = sipval[1, 0] * ext_wcs.binned
         kw2update['CTYPE1'] = 'RA---TAN-SIP'
         kw2update['CTYPE2'] = 'DEC--TAN-SIP'
         return kw2update
diff --git a/stwcs/updatewcs/det2im.py b/stwcs/updatewcs/det2im.py
index bddb37b..bb4cd9c 100644
--- a/stwcs/updatewcs/det2im.py
+++ b/stwcs/updatewcs/det2im.py
@@ -1,14 +1,13 @@
-from __future__ import absolute_import, division # confidence high
+from __future__ import absolute_import, division, print_function
 
-import numpy as np
 from astropy.io import fits
 from stsci.tools import fileutil
 
-from . import utils
-
-import logging, time
+import logging
+import time
 logger = logging.getLogger('stwcs.updatewcs.d2im')
 
+
 class DET2IMCorr(object):
     """
     Defines a Lookup table prior distortion correction as per WCS paper IV.
@@ -38,11 +37,11 @@ class DET2IMCorr(object):
                 Science file, for which a distortion correction in a NPOLFILE is available
 
         """
-        logger.info("\n\tStarting DET2IM: %s" %time.asctime())
+        logger.info("Starting DET2IM: {0}".format(time.asctime()))
         try:
             assert isinstance(fobj, fits.HDUList)
         except AssertionError:
-            logger.exception('\n\tInput must be a fits.HDUList object')
+            logger.exception('Input must be a fits.HDUList object')
             raise
 
         cls.applyDet2ImCorr(fobj)
@@ -84,7 +83,7 @@ class DET2IMCorr(object):
                         hdu = cls.createD2ImHDU(header, d2imfile=d2imfile,
                                                 wdvarr_ver=d2im_num_ext,
                                                 d2im_extname=ename[0],
-                                                data=ename[1],ccdchip=ccdchip)
+                                                data=ename[1], ccdchip=ccdchip)
                         if wcsdvarr_ind and d2im_num_ext in wcsdvarr_ind:
                             fobj[wcsdvarr_ind[d2im_num_ext]] = hdu
                         else:
@@ -108,7 +107,7 @@ class DET2IMCorr(object):
                 continue
             if ename == 'D2IMARR':
                 wcsd[fobj[e].header['EXTVER']] = e
-        logger.debug("A map of D2IMARR extensions %s" % wcsd)
+        logger.debug("A map of D2IMARR extensions {0}".format(wcsd))
         return wcsd
 
     getWCSIndex = classmethod(getWCSIndex)
@@ -118,17 +117,17 @@ class DET2IMCorr(object):
         Adds kw to sci extension to define WCSDVARR lookup table extensions
 
         """
-        if d2im_extname =='DX':
-            j=1
+        if d2im_extname == 'DX':
+            j = 1
         else:
-            j=2
-
-        d2imerror = 'D2IMERR%s' %j
-        d2imdis = 'D2IMDIS%s' %j
-        d2imext = 'D2IM%s.' %j + 'EXTVER'
-        d2imnaxes = 'D2IM%s.' %j +'NAXES'
-        d2imaxis1 = 'D2IM%s.' %j+'AXIS.1'
-        d2imaxis2 = 'D2IM%s.' %j+'AXIS.2'
+            j = 2
+
+        d2imerror = 'D2IMERR%s' % j
+        d2imdis = 'D2IMDIS%s' % j
+        d2imext = 'D2IM%s.' % j + 'EXTVER'
+        d2imnaxes = 'D2IM%s.' % j + 'NAXES'
+        d2imaxis1 = 'D2IM%s.' % j + 'AXIS.1'
+        d2imaxis2 = 'D2IM%s.' % j + 'AXIS.2'
         keys = [d2imerror, d2imdis, d2imext, d2imnaxes, d2imaxis1, d2imaxis2]
         values = {d2imerror: error_val,
                   d2imdis: 'Lookup',
@@ -154,7 +153,7 @@ class DET2IMCorr(object):
 
     addSciExtKw = classmethod(addSciExtKw)
 
-    def getData(cls,d2imfile, ccdchip):
+    def getData(cls, d2imfile, ccdchip):
         """
         Get the data arrays from the reference D2I files
         Make sure 'CCDCHIP' in the npolfile matches "CCDCHIP' in the science file.
@@ -162,8 +161,8 @@ class DET2IMCorr(object):
         xdata, ydata = (None, None)
         d2im = fits.open(d2imfile)
         for ext in d2im:
-            d2imextname  = ext.header.get('EXTNAME',"")
-            d2imccdchip  = ext.header.get('CCDCHIP',1)
+            d2imextname  = ext.header.get('EXTNAME', "")
+            d2imccdchip  = ext.header.get('CCDCHIP', 1)
             if d2imextname == 'DX' and d2imccdchip == ccdchip:
                 xdata = ext.data.copy()
                 continue
@@ -177,7 +176,7 @@ class DET2IMCorr(object):
     getData = classmethod(getData)
 
     def createD2ImHDU(cls, sciheader, d2imfile=None, wdvarr_ver=1,
-                      d2im_extname=None,data = None, ccdchip=1):
+                      d2im_extname=None, data=None, ccdchip=1):
         """
         Creates an HDU to be added to the file object.
         """
@@ -216,26 +215,26 @@ class DET2IMCorr(object):
         naxis = d2im[1].header['NAXIS']
         ccdchip = d2imextname
 
-        kw = { 'NAXIS': 'Size of the axis',
-               'CDELT': 'Coordinate increment along axis',
-               'CRPIX': 'Coordinate system reference pixel',
-               'CRVAL': 'Coordinate system value at reference pixel',
-               }
+        kw = {'NAXIS': 'Size of the axis',
+              'CDELT': 'Coordinate increment along axis',
+              'CRPIX': 'Coordinate system reference pixel',
+              'CRVAL': 'Coordinate system value at reference pixel',
+              }
 
         kw_comm1 = {}
         kw_val1 = {}
         for key in kw.keys():
-            for i in range(1, naxis+1):
+            for i in range(1, naxis + 1):
                 si = str(i)
-                kw_comm1[key+si] = kw[key]
+                kw_comm1[key + si] = kw[key]
 
-        for i in range(1, naxis+1):
+        for i in range(1, naxis + 1):
             si = str(i)
-            kw_val1['NAXIS'+si] = d2im_header.get('NAXIS'+si)
-            kw_val1['CDELT'+si] = d2im_header.get('CDELT'+si, 1.0) * sciheader.get('LTM'+si+'_'+si, 1)
-            kw_val1['CRPIX'+si] = d2im_header.get('CRPIX'+si, 0.0)
-            kw_val1['CRVAL'+si] = (d2im_header.get('CRVAL'+si, 0.0) - \
-                                   sciheader.get('LTV'+str(i), 0))
+            kw_val1['NAXIS' + si] = d2im_header.get('NAXIS' + si)
+            kw_val1['CDELT' + si] = d2im_header.get('CDELT' + si, 1.0) * sciheader.get('LTM' + si + '_' + si, 1)
+            kw_val1['CRPIX' + si] = d2im_header.get('CRPIX' + si, 0.0)
+            kw_val1['CRVAL' + si] = (d2im_header.get('CRVAL' + si, 0.0) -
+                                     sciheader.get('LTV' + str(i), 0))
         kw_comm0 = {'XTENSION': 'Image extension',
                     'BITPIX': 'IEEE floating point',
                     'NAXIS': 'Number of axes',
@@ -245,15 +244,15 @@ class DET2IMCorr(object):
                     'GCOUNT': 'One data group',
                     }
 
-        kw_val0 = { 'XTENSION': 'IMAGE',
-                    'BITPIX': -32,
-                    'NAXIS': naxis,
-                    'EXTNAME': 'D2IMARR',
-                    'EXTVER':  wdvarr_ver,
-                    'PCOUNT': 0,
-                    'GCOUNT': 1,
-                    'CCDCHIP': ccdchip,
-                }
+        kw_val0 = {'XTENSION': 'IMAGE',
+                   'BITPIX': -32,
+                   'NAXIS': naxis,
+                   'EXTNAME': 'D2IMARR',
+                   'EXTVER': wdvarr_ver,
+                   'PCOUNT': 0,
+                   'GCOUNT': 1,
+                   'CCDCHIP': ccdchip,
+                   }
         cdl = []
         for key in kw_comm0.keys():
             cdl.append((key, kw_val0[key], kw_comm0[key]))
@@ -266,8 +265,8 @@ class DET2IMCorr(object):
         for i, c in enumerate(d2im_phdr):
             if c == 'FILENAME':
                 start_indx = i
-            if c == '': # remove blanks from end of header
-                end_indx = i+1
+            if c == '':  # remove blanks from end of header
+                end_indx = i + 1
                 break
         if start_indx >= 0:
             for card in d2im_phdr.cards[start_indx:end_indx]:
@@ -287,7 +286,7 @@ class DET2IMCorr(object):
         if fobj[0].header['INSTRUME'] == 'ACS' and fobj[0].header['DETECTOR'] == 'WFC':
             ccdchip = fobj[extname, extver].header['CCDCHIP']
         elif fobj[0].header['INSTRUME'] == 'WFC3' and fobj[0].header['DETECTOR'] == 'UVIS':
-            ccdchip =  fobj[extname, extver].header['CCDCHIP']
+            ccdchip = fobj[extname, extver].header['CCDCHIP']
         elif fobj[0].header['INSTRUME'] == 'WFPC2':
             ccdchip = fobj[extname, extver].header['DETECTOR']
         elif fobj[0].header['INSTRUME'] == 'STIS':
diff --git a/stwcs/updatewcs/makewcs.py b/stwcs/updatewcs/makewcs.py
index 06c6f9c..4c6b3df 100644
--- a/stwcs/updatewcs/makewcs.py
+++ b/stwcs/updatewcs/makewcs.py
@@ -1,16 +1,16 @@
-from __future__ import absolute_import, division # confidence high
-
-import datetime
+from __future__ import absolute_import, division, print_function
 
 import numpy as np
-import logging, time
-from math import sin, sqrt, pow, cos, asin, atan2,pi
+import logging
+import time
+from math import sin, sqrt, pow, cos, asin, atan2, pi
 
 from stsci.tools import fileutil
 from . import utils
 
 logger = logging.getLogger(__name__)
 
+
 class MakeWCS(object):
     """
     Recompute basic WCS keywords based on PA_V3 and distortion model.
@@ -36,7 +36,8 @@ class MakeWCS(object):
     - Time dependent distortion correction is applied to both chips' V2/V3 values.
 
     """
-    tdd_xyref = {1: [2048, 3072], 2:[2048, 1024]}
+    tdd_xyref = {1: [2048, 3072], 2: [2048, 1024]}
+
     def updateWCS(cls, ext_wcs, ref_wcs):
         """
         recomputes the basic WCS kw
@@ -53,20 +54,20 @@ class MakeWCS(object):
         cls.uprefwcs(ext_wcs, ref_wcs, rv23_corr, ltvoff, offshift)
         cls.upextwcs(ext_wcs, ref_wcs, v23_corr, rv23_corr, ltvoff, offshift)
 
-        kw2update = {'CD1_1': ext_wcs.wcs.cd[0,0],
-                    'CD1_2': ext_wcs.wcs.cd[0,1],
-                    'CD2_1': ext_wcs.wcs.cd[1,0],
-                    'CD2_2': ext_wcs.wcs.cd[1,1],
-                    'CRVAL1': ext_wcs.wcs.crval[0],
-                    'CRVAL2': ext_wcs.wcs.crval[1],
-                    'CRPIX1': ext_wcs.wcs.crpix[0],
-                    'CRPIX2': ext_wcs.wcs.crpix[1],
-                    'IDCTAB': ext_wcs.idctab,
-                    'OCX10' : ext_wcs.idcmodel.cx[1,0],
-                    'OCX11' : ext_wcs.idcmodel.cx[1,1],
-                    'OCY10' : ext_wcs.idcmodel.cy[1,0],
-                    'OCY11' : ext_wcs.idcmodel.cy[1,1]
-            }
+        kw2update = {'CD1_1': ext_wcs.wcs.cd[0, 0],
+                     'CD1_2': ext_wcs.wcs.cd[0, 1],
+                     'CD2_1': ext_wcs.wcs.cd[1, 0],
+                     'CD2_2': ext_wcs.wcs.cd[1, 1],
+                     'CRVAL1': ext_wcs.wcs.crval[0],
+                     'CRVAL2': ext_wcs.wcs.crval[1],
+                     'CRPIX1': ext_wcs.wcs.crpix[0],
+                     'CRPIX2': ext_wcs.wcs.crpix[1],
+                     'IDCTAB': ext_wcs.idctab,
+                     'OCX10': ext_wcs.idcmodel.cx[1, 0],
+                     'OCX11': ext_wcs.idcmodel.cx[1, 1],
+                     'OCY10': ext_wcs.idcmodel.cy[1, 0],
+                     'OCY11': ext_wcs.idcmodel.cy[1, 1]
+                     }
         return kw2update
 
     updateWCS = classmethod(updateWCS)
@@ -82,41 +83,42 @@ class MakeWCS(object):
         if ltv1 != 0. or ltv2 != 0.:
             offsetx = ext_wcs.wcs.crpix[0] - ltv1 - ext_wcs.idcmodel.refpix['XREF']
             offsety = ext_wcs.wcs.crpix[1] - ltv2 - ext_wcs.idcmodel.refpix['YREF']
-            ext_wcs.idcmodel.shift(offsetx,offsety)
+            ext_wcs.idcmodel.shift(offsetx, offsety)
 
         fx, fy = ext_wcs.idcmodel.cx, ext_wcs.idcmodel.cy
 
         ext_wcs.setPscale()
-        tddscale = (ref_wcs.pscale/fx[1,1])
-        v2 = ext_wcs.idcmodel.refpix['V2REF'] + v23_corr[0,0] * tddscale
-        v3 = ext_wcs.idcmodel.refpix['V3REF'] - v23_corr[1,0] * tddscale
-        v2ref = ref_wcs.idcmodel.refpix['V2REF'] + rv23_corr[0,0] * tddscale
-        v3ref = ref_wcs.idcmodel.refpix['V3REF'] - rv23_corr[1,0] * tddscale
+        tddscale = (ref_wcs.pscale / fx[1, 1])
+        v2 = ext_wcs.idcmodel.refpix['V2REF'] + v23_corr[0, 0] * tddscale
+        v3 = ext_wcs.idcmodel.refpix['V3REF'] - v23_corr[1, 0] * tddscale
+        v2ref = ref_wcs.idcmodel.refpix['V2REF'] + rv23_corr[0, 0] * tddscale
+        v3ref = ref_wcs.idcmodel.refpix['V3REF'] - rv23_corr[1, 0] * tddscale
 
-        R_scale = ref_wcs.idcmodel.refpix['PSCALE']/3600.0
-        off = sqrt((v2-v2ref)**2 + (v3-v3ref)**2)/(R_scale*3600.0)
+        R_scale = ref_wcs.idcmodel.refpix['PSCALE'] / 3600.0
+        off = sqrt((v2 - v2ref) ** 2 + (v3 - v3ref) ** 2) / (R_scale * 3600.0)
 
         if v3 == v3ref:
-            theta=0.0
+            theta = 0.0
         else:
-            theta = atan2(ext_wcs.parity[0][0]*(v2-v2ref), ext_wcs.parity[1][1]*(v3-v3ref))
+            theta = atan2(ext_wcs.parity[0][0] * (v2 - v2ref),
+                          ext_wcs.parity[1][1] * (v3 - v3ref))
 
-        if ref_wcs.idcmodel.refpix['THETA']: theta += ref_wcs.idcmodel.refpix['THETA']*pi/180.0
+        if ref_wcs.idcmodel.refpix['THETA']: theta += ref_wcs.idcmodel.refpix['THETA'] * pi / 180.0
 
-        dX=(off*sin(theta)) + offshiftx
-        dY=(off*cos(theta)) + offshifty
+        dX = (off * sin(theta)) + offshiftx
+        dY = (off * cos(theta)) + offshifty
 
-        px = np.array([[dX,dY]])
+        px = np.array([[dX, dY]])
         newcrval = ref_wcs.wcs.p2s(px, 1)['world'][0]
         newcrpix = np.array([ext_wcs.idcmodel.refpix['XREF'] + ltvoffx,
-                                ext_wcs.idcmodel.refpix['YREF'] + ltvoffy])
+                             ext_wcs.idcmodel.refpix['YREF'] + ltvoffy])
         ext_wcs.wcs.crval = newcrval
         ext_wcs.wcs.crpix = newcrpix
         ext_wcs.wcs.set()
 
         # Create a small vector, in reference image pixel scale
-        delmat = np.array([[fx[1,1], fy[1,1]], \
-                              [fx[1,0], fy[1,0]]]) / R_scale/3600.
+        delmat = np.array([[fx[1, 1], fy[1, 1]],
+                           [fx[1, 0], fy[1, 0]]]) / R_scale / 3600.
 
         # Account for subarray offset
         # Angle of chip relative to chip
@@ -131,10 +133,10 @@ class MakeWCS(object):
         wc = ref_wcs.wcs.p2s((px + dxy), 1)['world']
 
         # Calculate the new CDs and convert to degrees
-        cd11 = utils.diff_angles(wc[0,0],newcrval[0])*cos(newcrval[1]*pi/180.0)
-        cd12 = utils.diff_angles(wc[1,0],newcrval[0])*cos(newcrval[1]*pi/180.0)
-        cd21 = utils.diff_angles(wc[0,1],newcrval[1])
-        cd22 = utils.diff_angles(wc[1,1],newcrval[1])
+        cd11 = utils.diff_angles(wc[0, 0], newcrval[0]) * cos(newcrval[1] * pi / 180.0)
+        cd12 = utils.diff_angles(wc[1, 0], newcrval[0]) * cos(newcrval[1] * pi / 180.0)
+        cd21 = utils.diff_angles(wc[0, 1], newcrval[1])
+        cd22 = utils.diff_angles(wc[1, 1], newcrval[1])
         cd = np.array([[cd11, cd12], [cd21, cd22]])
         ext_wcs.wcs.cd = cd
         ext_wcs.wcs.set()
@@ -151,39 +153,38 @@ class MakeWCS(object):
         if ref_wcs.ltv1 != 0. or ref_wcs.ltv2 != 0.:
             offsetx = ref_wcs.wcs.crpix[0] - ltv1 - ref_wcs.idcmodel.refpix['XREF']
             offsety = ref_wcs.wcs.crpix[1] - ltv2 - ref_wcs.idcmodel.refpix['YREF']
-            ref_wcs.idcmodel.shift(offsetx,offsety)
+            ref_wcs.idcmodel.shift(offsetx, offsety)
 
-        rfx, rfy = ref_wcs.idcmodel.cx, ref_wcs.idcmodel.cy
+        # rfx, rfy = ref_wcs.idcmodel.cx, ref_wcs.idcmodel.cy
 
-        offshift = offsh
+        # offshift = offsh
         dec = ref_wcs.wcs.crval[1]
-        tddscale = (ref_wcs.pscale/ref_wcs.idcmodel.cx[1,1])
-        rv23 = [ref_wcs.idcmodel.refpix['V2REF'] + (rv23_corr_tdd[0,0] *tddscale),
-            ref_wcs.idcmodel.refpix['V3REF'] - (rv23_corr_tdd[1,0] * tddscale)]
+        tddscale = (ref_wcs.pscale / ref_wcs.idcmodel.cx[1, 1])
+        rv23 = [ref_wcs.idcmodel.refpix['V2REF'] + (rv23_corr_tdd[0, 0] * tddscale),
+                ref_wcs.idcmodel.refpix['V3REF'] - (rv23_corr_tdd[1, 0] * tddscale)]
         # Get an approximate reference position on the sky
-        rref = np.array([[ref_wcs.idcmodel.refpix['XREF']+ltvoffx ,
-                            ref_wcs.idcmodel.refpix['YREF']+ltvoffy]])
+        rref = np.array([[ref_wcs.idcmodel.refpix['XREF'] + ltvoffx,
+                          ref_wcs.idcmodel.refpix['YREF'] + ltvoffy]])
 
         crval = ref_wcs.wcs.p2s(rref, 1)['world'][0]
         # Convert the PA_V3 orientation to the orientation at the aperture
         # This is for the reference chip only - we use this for the
         # reference tangent plane definition
         # It has the same orientation as the reference chip
-        pv = troll(ext_wcs.pav3,dec,rv23[0], rv23[1])
+        pv = troll(ext_wcs.pav3, dec, rv23[0], rv23[1])
         # Add the chip rotation angle
         if ref_wcs.idcmodel.refpix['THETA']:
             pv += ref_wcs.idcmodel.refpix['THETA']
 
-
         # Set values for the rest of the reference WCS
         ref_wcs.wcs.crval = crval
-        ref_wcs.wcs.crpix = np.array([0.0,0.0])+offsh
+        ref_wcs.wcs.crpix = np.array([0.0, 0.0]) + offsh
         parity = ref_wcs.parity
-        R_scale = ref_wcs.idcmodel.refpix['PSCALE']/3600.0
-        cd11 = parity[0][0] *  cos(pv*pi/180.0)*R_scale
-        cd12 = parity[0][0] * -sin(pv*pi/180.0)*R_scale
-        cd21 = parity[1][1] *  sin(pv*pi/180.0)*R_scale
-        cd22 = parity[1][1] *  cos(pv*pi/180.0)*R_scale
+        R_scale = ref_wcs.idcmodel.refpix['PSCALE'] / 3600.0
+        cd11 = parity[0][0] * cos(pv * pi / 180.0) * R_scale
+        cd12 = parity[0][0] * -sin(pv * pi / 180.0) * R_scale
+        cd21 = parity[1][1] * sin(pv * pi / 180.0) * R_scale
+        cd22 = parity[1][1] * cos(pv * pi / 180.0) * R_scale
 
         rcd = np.array([[cd11, cd12], [cd21, cd22]])
         ref_wcs.wcs.cd = rcd
@@ -191,9 +192,9 @@ class MakeWCS(object):
 
     uprefwcs = classmethod(uprefwcs)
 
-    def zero_point_corr(cls,hwcs):
+    def zero_point_corr(cls, hwcs):
         if hwcs.idcmodel.refpix['skew_coeffs'] is not None and 'TDD_CY_BETA' in hwcs.idcmodel.refpix['skew_coeffs']:
-            v23_corr = np.array([[0.],[0.]])
+            v23_corr = np.array([[0.], [0.]])
             return v23_corr
         else:
             try:
@@ -202,15 +203,17 @@ class MakeWCS(object):
             except KeyError:
                 alpha = 0.0
                 beta = 0.0
-                v23_corr = np.array([[0.],[0.]])
-                logger.debug("\n\tTDD Zero point correction for chip %s defaulted to: %s" % (hwcs.chip, v23_corr))
+                v23_corr = np.array([[0.], [0.]])
+                logger.debug("TDD Zero point correction for chip"
+                             "{0} defaulted to: {1}".format(hwcs.chip, v23_corr))
                 return v23_corr
 
         tdd = np.array([[beta, alpha], [alpha, -beta]])
-        mrotp = fileutil.buildRotMatrix(2.234529)/2048.
-        xy0 = np.array([[cls.tdd_xyref[hwcs.chip][0]-2048.], [cls.tdd_xyref[hwcs.chip][1]-2048.]])
-        v23_corr = np.dot(mrotp,np.dot(tdd,xy0)) * 0.05
-        logger.debug("\n\tTDD Zero point correction for chip %s: %s" % (hwcs.chip, v23_corr))
+        mrotp = fileutil.buildRotMatrix(2.234529) / 2048.
+        xy0 = np.array([[cls.tdd_xyref[hwcs.chip][0] - 2048.],
+                        [cls.tdd_xyref[hwcs.chip][1] - 2048.]])
+        v23_corr = np.dot(mrotp, np.dot(tdd, xy0)) * 0.05
+        logger.debug("TDD Zero point correction for chip {0}: {1}".format(hwcs.chip, v23_corr))
         return v23_corr
 
     zero_point_corr = classmethod(zero_point_corr)
@@ -258,16 +261,16 @@ def troll(roll, dec, v2, v3):
     _v3 = np.deg2rad(v3 / 3600.)
 
     # compute components
-    sin_rho = sqrt((pow(sin(_v2),2)+pow(sin(_v3),2)) - (pow(sin(_v2),2)*pow(sin(_v3),2)))
+    sin_rho = sqrt((pow(sin(_v2), 2) + pow(sin(_v3), 2)) - (pow(sin(_v2), 2) * pow(sin(_v3), 2)))
     rho = asin(sin_rho)
-    beta = asin(sin(_v3)/sin_rho)
+    beta = asin(sin(_v3) / sin_rho)
     if _v2 < 0: beta = pi - beta
-    gamma = asin(sin(_v2)/sin_rho)
+    gamma = asin(sin(_v2) / sin_rho)
     if _v3 < 0: gamma = pi - gamma
-    A = pi/2. + _roll - beta
-    B = atan2( sin(A)*cos(_dec), (sin(_dec)*sin_rho - cos(_dec)*cos(rho)*cos(A)))
+    A = pi / 2. + _roll - beta
+    B = atan2(sin(A) * cos(_dec), (sin(_dec) * sin_rho - cos(_dec) * cos(rho) * cos(A)))
 
     # compute final value
-    troll = np.rad2deg(pi - (gamma+B))
+    troll = np.rad2deg(pi - (gamma + B))
 
     return troll
diff --git a/stwcs/updatewcs/npol.py b/stwcs/updatewcs/npol.py
index 33579f0..9c88150 100644
--- a/stwcs/updatewcs/npol.py
+++ b/stwcs/updatewcs/npol.py
@@ -1,15 +1,16 @@
-from __future__ import absolute_import, division # confidence high
+from __future__ import absolute_import, division, print_function
 
-import logging, time
+import logging
+import time
 
 import numpy as np
 from astropy.io import fits
 
 from stsci.tools import fileutil
-from . import utils
 
 logger = logging.getLogger('stwcs.updatewcs.npol')
 
+
 class NPOLCorr(object):
     """
     Defines a Lookup table prior distortion correction as per WCS paper IV.
@@ -43,7 +44,7 @@ class NPOLCorr(object):
             Science file, for which a distortion correction in a NPOLFILE is available
 
         """
-        logger.info("\n\tStarting NPOL: %s" %time.asctime())
+        logger.info("\n\tStarting NPOL: %s" % time.asctime())
         try:
             assert isinstance(fobj, fits.HDUList)
         except AssertionError:
@@ -79,28 +80,28 @@ class NPOLCorr(object):
                 header = ext.header
                 # get the data arrays from the reference file and transform
                 # them for use with SIP
-                dx,dy = cls.getData(nplfile, ccdchip)
+                dx, dy = cls.getData(nplfile, ccdchip)
                 idccoeffs = cls.getIDCCoeffs(header)
 
                 if idccoeffs is not None:
-                    dx, dy = cls.transformData(dx,dy, idccoeffs)
+                    dx, dy = cls.transformData(dx, dy, idccoeffs)
 
                 # Determine EXTVER for the WCSDVARR extension from the
                 # NPL file (EXTNAME, EXTVER) kw.
                 # This is used to populate DPj.EXTVER kw
-                wcsdvarr_x_version = 2 * extversion -1
+                wcsdvarr_x_version = 2 * extversion - 1
                 wcsdvarr_y_version = 2 * extversion
-                for ename in zip(['DX', 'DY'], [wcsdvarr_x_version,wcsdvarr_y_version],[dx, dy]):
+                for ename in zip(['DX', 'DY'], [wcsdvarr_x_version, wcsdvarr_y_version], [dx, dy]):
                     error_val = ename[2].max()
                     cls.addSciExtKw(header, wdvarr_ver=ename[1], npol_extname=ename[0], error_val=error_val)
-                    hdu = cls.createNpolHDU(header, npolfile=nplfile, \
-                        wdvarr_ver=ename[1], npl_extname=ename[0], data=ename[2],ccdchip=ccdchip)
+                    hdu = cls.createNpolHDU(header, npolfile=nplfile,
+                                            wdvarr_ver=ename[1], npl_extname=ename[0],
+                                            data=ename[2], ccdchip=ccdchip)
                     if wcsdvarr_ind:
                         fobj[wcsdvarr_ind[ename[1]]] = hdu
                     else:
                         fobj.append(hdu)
 
-
     applyNPOLCorr = classmethod(applyNPOLCorr)
 
     def getWCSIndex(cls, fobj):
@@ -129,17 +130,17 @@ class NPOLCorr(object):
         Adds kw to sci extension to define WCSDVARR lookup table extensions
 
         """
-        if npol_extname =='DX':
-            j=1
+        if npol_extname == 'DX':
+            j = 1
         else:
-            j=2
-
-        cperror = 'CPERR%s' %j
-        cpdis = 'CPDIS%s' %j
-        dpext = 'DP%s.' %j + 'EXTVER'
-        dpnaxes = 'DP%s.' %j +'NAXES'
-        dpaxis1 = 'DP%s.' %j+'AXIS.1'
-        dpaxis2 = 'DP%s.' %j+'AXIS.2'
+            j = 2
+
+        cperror = 'CPERR%s' % j
+        cpdis = 'CPDIS%s' % j
+        dpext = 'DP%s.' % j + 'EXTVER'
+        dpnaxes = 'DP%s.' % j + 'NAXES'
+        dpaxis1 = 'DP%s.' % j + 'AXIS.1'
+        dpaxis2 = 'DP%s.' % j + 'AXIS.2'
         keys = [cperror, cpdis, dpext, dpnaxes, dpaxis1, dpaxis2]
         values = {cperror: error_val,
                   cpdis: 'Lookup',
@@ -165,15 +166,15 @@ class NPOLCorr(object):
 
     addSciExtKw = classmethod(addSciExtKw)
 
-    def getData(cls,nplfile, ccdchip):
+    def getData(cls, nplfile, ccdchip):
         """
         Get the data arrays from the reference NPOL files
         Make sure 'CCDCHIP' in the npolfile matches "CCDCHIP' in the science file.
         """
         npl = fits.open(nplfile)
         for ext in npl:
-            nplextname  = ext.header.get('EXTNAME',"")
-            nplccdchip  = ext.header.get('CCDCHIP',1)
+            nplextname  = ext.header.get('EXTNAME', "")
+            nplccdchip  = ext.header.get('CCDCHIP', 1)
             if nplextname == 'DX' and nplccdchip == ccdchip:
                 xdata = ext.data.copy()
                 continue
@@ -192,7 +193,7 @@ class NPOLCorr(object):
         """
         ndx, ndy = np.dot(coeffs, [dx.ravel(), dy.ravel()]).astype(np.float32)
         ndx.shape = dx.shape
-        ndy.shape=dy.shape
+        ndy.shape = dy.shape
         return ndx, ndy
 
     transformData = classmethod(transformData)
@@ -206,7 +207,7 @@ class NPOLCorr(object):
             ocx11 = header['OCX11']
             ocy10 = header['OCY10']
             ocy11 = header['OCY11']
-            coeffs = np.array([[ocx11, ocx10], [ocy11,ocy10]], dtype=np.float32)
+            coeffs = np.array([[ocx11, ocx10], [ocy11, ocy10]], dtype=np.float32)
         except KeyError:
             logger.exception('\n\tFirst order IDCTAB coefficients are not available. \n\
             Cannot convert SIP to IDC coefficients.')
@@ -217,15 +218,17 @@ class NPOLCorr(object):
             logger.exception("IDCSCALE not found in header - setting it to 1.")
             idcscale = 1
 
-        return np.linalg.inv(coeffs/idcscale)
+        return np.linalg.inv(coeffs / idcscale)
 
     getIDCCoeffs = classmethod(getIDCCoeffs)
 
-    def createNpolHDU(cls, sciheader, npolfile=None, wdvarr_ver=1, npl_extname=None,data = None, ccdchip=1):
+    def createNpolHDU(cls, sciheader, npolfile=None, wdvarr_ver=1, npl_extname=None,
+                      data=None, ccdchip=1):
         """
         Creates an HDU to be added to the file object.
         """
-        hdr = cls.createNpolHdr(sciheader, npolfile=npolfile, wdvarr_ver=wdvarr_ver, npl_extname=npl_extname, ccdchip=ccdchip)
+        hdr = cls.createNpolHdr(sciheader, npolfile=npolfile, wdvarr_ver=wdvarr_ver,
+                                npl_extname=npl_extname, ccdchip=ccdchip)
         hdu = fits.ImageHDU(header=hdr, data=data)
         return hdu
 
@@ -256,29 +259,29 @@ class NPOLCorr(object):
         npl.close()
 
         naxis = npl[1].header['NAXIS']
-        ccdchip = nplextname #npol_header['CCDCHIP']
+        ccdchip = nplextname  # npol_header['CCDCHIP']
 
-        kw = { 'NAXIS': 'Size of the axis',
-               'CDELT': 'Coordinate increment along axis',
-               'CRPIX': 'Coordinate system reference pixel',
-               'CRVAL': 'Coordinate system value at reference pixel',
-               }
+        kw = {'NAXIS': 'Size of the axis',
+              'CDELT': 'Coordinate increment along axis',
+              'CRPIX': 'Coordinate system reference pixel',
+              'CRVAL': 'Coordinate system value at reference pixel',
+              }
 
         kw_comm1 = {}
         kw_val1 = {}
         for key in kw.keys():
-            for i in range(1, naxis+1):
+            for i in range(1, naxis + 1):
                 si = str(i)
-                kw_comm1[key+si] = kw[key]
+                kw_comm1[key + si] = kw[key]
 
-        for i in range(1, naxis+1):
+        for i in range(1, naxis + 1):
             si = str(i)
-            kw_val1['NAXIS'+si] = npol_header.get('NAXIS'+si)
-            kw_val1['CDELT'+si] = npol_header.get('CDELT'+si, 1.0) * \
-                                  sciheader.get('LTM'+si+'_'+si, 1)
-            kw_val1['CRPIX'+si] = npol_header.get('CRPIX'+si, 0.0)
-            kw_val1['CRVAL'+si] = (npol_header.get('CRVAL'+si, 0.0) - \
-                                  sciheader.get('LTV'+str(i), 0))
+            kw_val1['NAXIS' + si] = npol_header.get('NAXIS' + si)
+            kw_val1['CDELT' + si] = npol_header.get('CDELT' + si, 1.0) * \
+                sciheader.get('LTM' + si + '_' + si, 1)
+            kw_val1['CRPIX' + si] = npol_header.get('CRPIX' + si, 0.0)
+            kw_val1['CRVAL' + si] = (npol_header.get('CRVAL' + si, 0.0) -
+                                     sciheader.get('LTV' + str(i), 0))
 
         kw_comm0 = {'XTENSION': 'Image extension',
                     'BITPIX': 'IEEE floating point',
@@ -289,15 +292,15 @@ class NPOLCorr(object):
                     'GCOUNT': 'One data group',
                     }
 
-        kw_val0 = { 'XTENSION': 'IMAGE',
-                    'BITPIX': -32,
-                    'NAXIS': naxis,
-                    'EXTNAME': 'WCSDVARR',
-                    'EXTVER':  wdvarr_ver,
-                    'PCOUNT': 0,
-                    'GCOUNT': 1,
-                    'CCDCHIP': ccdchip,
-                }
+        kw_val0 = {'XTENSION': 'IMAGE',
+                   'BITPIX': -32,
+                   'NAXIS': naxis,
+                   'EXTNAME': 'WCSDVARR',
+                   'EXTVER': wdvarr_ver,
+                   'PCOUNT': 0,
+                   'GCOUNT': 1,
+                   'CCDCHIP': ccdchip,
+                   }
         cdl = []
         for key in kw_comm0.keys():
             cdl.append((key, kw_val0[key], kw_comm0[key]))
@@ -310,11 +313,11 @@ class NPOLCorr(object):
         for i, c in enumerate(npol_phdr):
             if c == 'FILENAME':
                 start_indx = i
-            if c == '': # remove blanks from end of header
-                end_indx = i+1
+            if c == '':  # remove blanks from end of header
+                end_indx = i + 1
                 break
         if start_indx >= 0:
-            for card in npol_phdr.cards[start_indx:end_indx]:
+            for card in npol_phdr.cards[start_indx: end_indx]:
                 cdl.append(card)
 
         hdr = fits.Header(cards=cdl)
@@ -331,7 +334,7 @@ class NPOLCorr(object):
         if fobj[0].header['INSTRUME'] == 'ACS' and fobj[0].header['DETECTOR'] == 'WFC':
             ccdchip = fobj[extname, extver].header['CCDCHIP']
         elif fobj[0].header['INSTRUME'] == 'WFC3' and fobj[0].header['DETECTOR'] == 'UVIS':
-            ccdchip =  fobj[extname, extver].header['CCDCHIP']
+            ccdchip = fobj[extname, extver].header['CCDCHIP']
         elif fobj[0].header['INSTRUME'] == 'WFPC2':
             ccdchip = fobj[extname, extver].header['DETECTOR']
         elif fobj[0].header['INSTRUME'] == 'STIS':
diff --git a/stwcs/updatewcs/utils.py b/stwcs/updatewcs/utils.py
index ebfc701..8c8d416 100644
--- a/stwcs/updatewcs/utils.py
+++ b/stwcs/updatewcs/utils.py
@@ -1,4 +1,4 @@
-from __future__ import division # confidence high
+from __future__ import absolute_import, division, print_function
 import os
 from astropy.io import fits
 from stsci.tools import fileutil
@@ -7,7 +7,7 @@ import logging
 logger = logging.getLogger("stwcs.updatewcs.utils")
 
 
-def diff_angles(a,b):
+def diff_angles(a, b):
     """
     Perform angle subtraction a-b taking into account
     small-angle differences across 360degree line.
@@ -23,6 +23,7 @@ def diff_angles(a,b):
 
     return diff
 
+
 def getBinning(fobj, extver=1):
     # Return the binning factor
     binned = 1
@@ -30,9 +31,10 @@ def getBinning(fobj, extver=1):
         mode = fobj[0].header.get('MODE', "")
         if mode == 'AREA': binned = 2
     else:
-        binned = fobj['SCI', extver].header.get('BINAXIS',1)
+        binned = fobj['SCI', extver].header.get('BINAXIS', 1)
     return binned
 
+
 def updateNEXTENDKw(fobj):
     """
     Updates PRIMARY header with correct value for NEXTEND, if present.
@@ -44,9 +46,10 @@ def updateNEXTENDKw(fobj):
 
     """
     if 'nextend' in fobj[0].header:
-        fobj[0].header['nextend'] = len(fobj) -1
+        fobj[0].header['nextend'] = len(fobj) - 1
+
 
-def extract_rootname(kwvalue,suffix=""):
+def extract_rootname(kwvalue, suffix=""):
     """ Returns the rootname from a full reference filename
 
         If a non-valid value (any of ['','N/A','NONE','INDEF',None]) is input,
@@ -55,13 +58,13 @@ def extract_rootname(kwvalue,suffix=""):
         This function will also replace any 'suffix' specified with a blank.
     """
     # check to see whether a valid kwvalue has been provided as input
-    if kwvalue.strip() in ['','N/A','NONE','INDEF',None]:
-        return 'NONE' # no valid value, so return 'NONE'
+    if kwvalue.strip() in ['', 'N/A', 'NONE', 'INDEF', None]:
+        return 'NONE'  # no valid value, so return 'NONE'
 
     # for a valid kwvalue, parse out the rootname
     # strip off any environment variable from input filename, if any are given
     if '$' in kwvalue:
-        fullval = kwvalue[kwvalue.find('$')+1:]
+        fullval = kwvalue[kwvalue.find('$') + 1: ]
     else:
         fullval = kwvalue
     # Extract filename without path from kwvalue
@@ -71,10 +74,11 @@ def extract_rootname(kwvalue,suffix=""):
     rootname = fileutil.buildNewRootname(fname)
 
     # Now, remove any known suffix from rootname
-    rootname = rootname.replace(suffix,'')
+    rootname = rootname.replace(suffix, '')
     return rootname.strip()
 
-def construct_distname(fobj,wcsobj):
+
+def construct_distname(fobj, wcsobj):
     """
     This function constructs the value for the keyword 'DISTNAME'.
     It relies on the reference files specified by the keywords 'IDCTAB',
@@ -85,8 +89,8 @@ def construct_distname(fobj,wcsobj):
     and have a value of 'NONE' if no reference files are specified.
     """
     idcname = extract_rootname(fobj[0].header.get('IDCTAB', "NONE"),
-                                suffix='_idc')
-    if (idcname is None or idcname=='NONE') and wcsobj.sip is not None:
+                               suffix='_idc')
+    if (idcname is None or idcname == 'NONE') and wcsobj.sip is not None:
         idcname = 'UNKNOWN'
 
     npolname, npolfile = build_npolname(fobj)
@@ -99,29 +103,30 @@ def construct_distname(fobj,wcsobj):
 
     sipname, idctab = build_sipname(fobj)
 
-    distname = build_distname(sipname,npolname,d2imname)
-    return {'DISTNAME':distname,'SIPNAME':sipname}
+    distname = build_distname(sipname, npolname, d2imname)
+    return {'DISTNAME': distname, 'SIPNAME': sipname}
+
 
-def build_distname(sipname,npolname,d2imname):
+def build_distname(sipname, npolname, d2imname):
     """
     Core function to build DISTNAME keyword value without the HSTWCS input.
     """
-
     distname = sipname.strip()
     if npolname != 'NONE' or d2imname != 'NONE':
         if d2imname != 'NONE':
-            distname+= '-'+npolname.strip() + '-'+d2imname.strip()
+            distname += '-' + npolname.strip() + '-' + d2imname.strip()
         else:
-            distname+='-'+npolname.strip()
+            distname += '-' + npolname.strip()
 
     return distname
 
-def build_default_wcsname(idctab):
 
-    idcname = extract_rootname(idctab,suffix='_idc')
+def build_default_wcsname(idctab):
+    idcname = extract_rootname(idctab, suffix='_idc')
     wcsname = 'IDC_' + idcname
     return wcsname
 
+
 def build_sipname(fobj, fname=None, sipname=None):
     """
     Build a SIPNAME from IDCTAB
@@ -141,10 +146,10 @@ def build_sipname(fobj, fname=None, sipname=None):
     """
     try:
         idctab = fobj[0].header['IDCTAB']
-        idcname = extract_rootname(idctab,suffix='_idc')
+        idcname = extract_rootname(idctab, suffix='_idc')
     except KeyError:
         idctab = 'N/A'
-        idcname= 'N/A'
+        idcname = 'N/A'
     if not fname:
         try:
             fname = fobj.filename()
@@ -161,7 +166,7 @@ def build_sipname(fobj, fname=None, sipname=None):
                     rootname = fobj[0].header['rootname']
                 except KeyError:
                     rootname = fname
-                sipname = rootname +'_'+ idcname
+                sipname = rootname + '_' + idcname
             else:
                 if 'A_ORDER' in fobj[1].header or 'B_ORDER' in fobj[1].header:
                     sipname = 'UNKNOWN'
@@ -170,6 +175,7 @@ def build_sipname(fobj, fname=None, sipname=None):
 
     return sipname, idctab
 
+
 def build_npolname(fobj, npolfile=None):
     """
     Build a NPOLNAME from NPOLFILE
@@ -203,6 +209,7 @@ def build_npolname(fobj, npolfile=None):
             npolname = 'NOMODEL'
     return npolname, npolfile
 
+
 def build_d2imname(fobj, d2imfile=None):
     """
     Build a D2IMNAME from D2IMFILE
@@ -227,11 +234,11 @@ def build_d2imname(fobj, d2imfile=None):
                 d2imname = 'UNKNOWN'
             else:
                 d2imname = 'NOMODEL'
-        d2imname = extract_rootname(d2imfile,suffix='_d2i')
+        d2imname = extract_rootname(d2imfile, suffix='_d2i')
         if d2imname == 'NONE':
             d2imname = 'NOMODEL'
     else:
-        d2imname = extract_rootname(d2imfile,suffix='_d2i')
+        d2imname = extract_rootname(d2imfile, suffix='_d2i')
         if d2imname == 'NONE':
             d2imname = 'NOMODEL'
     return d2imname, d2imfile
diff --git a/stwcs/updatewcs/wfpc2_dgeo.py b/stwcs/updatewcs/wfpc2_dgeo.py
index e57bb5c..b76198a 100644
--- a/stwcs/updatewcs/wfpc2_dgeo.py
+++ b/stwcs/updatewcs/wfpc2_dgeo.py
@@ -1,6 +1,7 @@
 """ wfpc2_dgeo - Functions to convert WFPC2 DGEOFILE into D2IMFILE
 
 """
+from __future__ import absolute_import, division, print_function
 import os
 import datetime
 
@@ -13,6 +14,7 @@ from stsci.tools import fileutil
 import logging
 logger = logging.getLogger("stwcs.updatewcs.apply_corrections")
 
+
 def update_wfpc2_d2geofile(filename, fhdu=None):
     """
     Creates a D2IMFILE from the DGEOFILE for a WFPC2 image (input), and
@@ -35,7 +37,7 @@ def update_wfpc2_d2geofile(filename, fhdu=None):
         image header will be updated/added to point to this newly created file.
 
     """
-    
+
     close_fhdu = False
     if fhdu is None:
         fhdu = fileutil.openImage(filename, mode='update')
@@ -48,7 +50,7 @@ def update_wfpc2_d2geofile(filename, fhdu=None):
             dgeofile = fhdu['PRIMARY'].header.get('ODGEOFIL', None)
         logger.info('Converting DGEOFILE %s into D2IMFILE...' % dgeofile)
         rootname = filename[:filename.find('.fits')]
-        d2imfile = convert_dgeo_to_d2im(dgeofile,rootname)
+        d2imfile = convert_dgeo_to_d2im(dgeofile, rootname)
         fhdu['PRIMARY'].header['ODGEOFIL'] = dgeofile
         fhdu['PRIMARY'].header['DGEOFILE'] = 'N/A'
         fhdu['PRIMARY'].header['D2IMFILE'] = d2imfile
@@ -67,25 +69,26 @@ def update_wfpc2_d2geofile(filename, fhdu=None):
     # (multidrizzle clean=True mode of operation)
     return d2imfile
 
-def convert_dgeo_to_d2im(dgeofile,output,clobber=True):
+
+def convert_dgeo_to_d2im(dgeofile, output, clobber=True):
     """ Routine that converts the WFPC2 DGEOFILE into a D2IMFILE.
     """
     dgeo = fileutil.openImage(dgeofile)
-    outname = output+'_d2im.fits'
+    outname = output + '_d2im.fits'
 
     removeFileSafely(outname)
-    data = np.array([dgeo['dy',1].data[:,0]])
+    data = np.array([dgeo['dy', 1].data[:, 0]])
     scihdu = fits.ImageHDU(data=data)
     dgeo.close()
     # add required keywords for D2IM header
     scihdu.header['EXTNAME'] = ('DY', 'Extension name')
     scihdu.header['EXTVER'] = (1, 'Extension version')
-    fits_str = 'PYFITS Version '+str(astropy.__version__)
+    fits_str = 'PYFITS Version ' + str(astropy.__version__)
     scihdu.header['ORIGIN'] = (fits_str, 'FITS file originator')
     scihdu.header['INHERIT'] = (False, 'Inherits global header')
 
     dnow = datetime.datetime.now()
-    scihdu.header['DATE'] = (str(dnow).replace(' ','T'),
+    scihdu.header['DATE'] = (str(dnow).replace(' ', 'T'),
                              'Date FITS file was generated')
 
     scihdu.header['CRPIX1'] = (0, 'Distortion array reference pixel')
@@ -116,7 +119,7 @@ def convert_dgeo_to_d2im(dgeofile,output,clobber=True):
     return outname
 
 
-def removeFileSafely(filename,clobber=True):
+def removeFileSafely(filename, clobber=True):
     """ Delete the file specified, but only if it exists and clobber is True.
     """
     if filename is not None and filename.strip() != '':
diff --git a/stwcs/wcsutil/__init__.py b/stwcs/wcsutil/__init__.py
index 65280be..d9d21c5 100644
--- a/stwcs/wcsutil/__init__.py
+++ b/stwcs/wcsutil/__init__.py
@@ -1,4 +1,4 @@
-from __future__ import absolute_import, print_function # confidence high
+from __future__ import absolute_import, print_function
 
 from .altwcs import *
 from .hstwcs import HSTWCS
diff --git a/stwcs/wcsutil/altwcs.py b/stwcs/wcsutil/altwcs.py
index 5dc7dd6..64cdc87 100644
--- a/stwcs/wcsutil/altwcs.py
+++ b/stwcs/wcsutil/altwcs.py
@@ -1,7 +1,6 @@
-from __future__ import division, print_function # confidence high
-import os
-import string
+from __future__ import absolute_import, division, print_function
 
+import string
 import numpy as np
 from astropy import wcs as pywcs
 from astropy.io import fits
@@ -9,9 +8,11 @@ from stsci.tools import fileutil as fu
 
 altwcskw = ['WCSAXES', 'CRVAL', 'CRPIX', 'PC', 'CDELT', 'CD', 'CTYPE', 'CUNIT',
             'PV', 'PS']
-altwcskw_extra = ['LATPOLE','LONPOLE','RESTWAV','RESTFRQ']
+altwcskw_extra = ['LATPOLE', 'LONPOLE', 'RESTWAV', 'RESTFRQ']
 
 # file operations
+
+
 def archiveWCS(fname, ext, wcskey=" ", wcsname=" ", reusekey=False):
     """
     Copy the primary WCS to the header as an alternate WCS
@@ -77,7 +78,7 @@ def archiveWCS(fname, ext, wcskey=" ", wcsname=" ", reusekey=False):
         closefobj(fname, f)
         raise KeyError("Wcskey %s is aready used. \
         Run archiveWCS() with reusekey=True to overwrite this alternate WCS. \
-        Alternatively choose another wcskey with altwcs.available_wcskeys()." %wcskey)
+        Alternatively choose another wcskey with altwcs.available_wcskeys()." % wcskey)
     elif wcskey == " ":
         # wcsname exists, overwrite it if reuse is True or get the next key
         if wcsname.strip() in wcsnames(f[wcsext].header).values():
@@ -89,13 +90,13 @@ def archiveWCS(fname, ext, wcskey=" ", wcsname=" ", reusekey=False):
                     wkey = next_wcskey(f[wcsext].header)
                 elif wkey is None:
                     closefobj(fname, f)
-                    raise KeyError("Could not get a valid wcskey from wcsname %s" %wcsname)
+                    raise KeyError("Could not get a valid wcskey from wcsname %s" % wcsname)
             else:
                 closefobj(fname, f)
                 raise KeyError("Wcsname %s is aready used. \
                 Run archiveWCS() with reusekey=True to overwrite this alternate WCS. \
                 Alternatively choose another wcskey with altwcs.available_wcskeys() or\
-                choose another wcsname." %wcsname)
+                choose another wcsname." % wcsname)
         else:
             wkey = next_wcskey(f[wcsext].header)
             if wcsname.strip():
@@ -103,7 +104,7 @@ def archiveWCS(fname, ext, wcskey=" ", wcsname=" ", reusekey=False):
             else:
                 # determine which WCSNAME needs to be replicated in archived WCS
                 wnames = wcsnames(f[wcsext].header)
-                if 'O' in wnames: del wnames['O'] # we don't want OPUS/original
+                if 'O' in wnames: del wnames['O']  # we don't want OPUS/original
                 if len(wnames) > 0:
                     if ' ' in wnames:
                         wname = wnames[' ']
@@ -139,15 +140,16 @@ def archiveWCS(fname, ext, wcskey=" ", wcsname=" ", reusekey=False):
         f[e].header[wcsnamekey] = wname
 
         try:
-            old_wcsname=hwcs.pop('WCSNAME')
+            old_wcsname = hwcs.pop('WCSNAME')
         except:
             pass
 
         for k in hwcs.keys():
-            key = k[:7] + wkey
+            key = k[: 7] + wkey
             f[e].header[key] = hwcs[k]
     closefobj(fname, f)
 
+
 def restore_from_to(f, fromext=None, toext=None, wcskey=" ", wcsname=" "):
     """
     Copy an alternate WCS from one extension as a primary WCS of another extension
@@ -188,14 +190,14 @@ def restore_from_to(f, fromext=None, toext=None, wcskey=" ", wcsname=" "):
         raise ValueError("Input parameters problem")
 
     # Interpret input 'ext' value to get list of extensions to process
-    #ext = _buildExtlist(fobj, ext)
+    # ext = _buildExtlist(fobj, ext)
 
     if isinstance(toext, str):
         toext = [toext]
 
     # the case of an HDUList object in memory without an associated file
 
-    #if fobj.filename() is not None:
+    # if fobj.filename() is not None:
     #        name = fobj.filename()
 
     simplefits = fu.isFits(fobj)[1] is 'simple'
@@ -221,14 +223,15 @@ def restore_from_to(f, fromext=None, toext=None, wcskey=" ", wcsname=" "):
     if not countext:
         raise KeyError("File does not have extension with extname %s", fromext)
     else:
-        for i in range(1, countext+1):
+        for i in range(1, countext + 1):
             for toe in toext:
                 _restore(fobj, fromextnum=i, fromextnam=fromext, toextnum=i, toextnam=toe, ukey=wkey)
 
     if fobj.filename() is not None:
-        #fobj.writeto(name)
+        # fobj.writeto(name)
         closefobj(f, fobj)
 
+
 def restoreWCS(f, ext, wcskey=" ", wcsname=" "):
     """
     Copy a WCS with key "WCSKEY" to the primary WCS
@@ -272,9 +275,6 @@ def restoreWCS(f, ext, wcskey=" ", wcsname=" "):
 
     # the case of an HDUList object in memory without an associated file
 
-    #if fobj.filename() is not None:
-    #        name = fobj.filename()
-
     simplefits = fu.isFits(fobj)[1] is 'simple'
     if simplefits:
         wcskeyext = 0
@@ -297,6 +297,7 @@ def restoreWCS(f, ext, wcskey=" ", wcsname=" "):
     if fobj.filename() is not None:
         closefobj(f, fobj)
 
+
 def deleteWCS(fname, ext, wcskey=" ", wcsname=" "):
     """
     Delete an alternate WCS defined with wcskey.
@@ -351,7 +352,7 @@ def deleteWCS(fname, ext, wcskey=" ", wcsname=" "):
     prexts = []
     for i in ext:
         hdr = fobj[i].header
-        hwcs = readAltWCS(fobj,i,wcskey=wkey)
+        hwcs = readAltWCS(fobj, i, wcskey=wkey)
         if hwcs is None:
             continue
         for k in hwcs[::-1]:
@@ -363,6 +364,7 @@ def deleteWCS(fname, ext, wcskey=" ", wcsname=" "):
         print("Did not find WCS with key %s in any of the extensions" % wkey)
     closefobj(fname, fobj)
 
+
 def _buildExtlist(fobj, ext):
     """
     Utility function to interpret the provided value of 'ext' and return a list
@@ -378,8 +380,8 @@ def _buildExtlist(fobj, ext):
             If a string is provided, it should specify the EXTNAME of extensions
             with WCSs to be archived
     """
-    if not isinstance(ext,list):
-        if isinstance(ext,str):
+    if not isinstance(ext, list):
+        if isinstance(ext, str):
             extstr = ext
             ext = []
             for extn in range(1, len(fobj)):
@@ -391,6 +393,7 @@ def _buildExtlist(fobj, ext):
             raise KeyError("Valid extensions in 'ext' parameter need to be specified.")
     return ext
 
+
 def _restore(fobj, ukey, fromextnum,
              toextnum=None, fromextnam=None, toextnam=None, verbose=True):
     """
@@ -415,7 +418,7 @@ def _restore(fobj, ukey, fromextnum,
         if toextnam:
             toextension = (toextnam, toextnum)
         else:
-            toextension =toextnum
+            toextension = toextnum
     else:
         toextension = fromextension
 
@@ -445,34 +448,38 @@ def _restore(fobj, ukey, fromextnum,
         fobj[toextension].header['TDDALPHA'] = 0.0
         fobj[toextension].header['TDDBETA'] = 0.0
     if 'ORIENTAT' in fobj[toextension].header:
-        norient = np.rad2deg(np.arctan2(hwcs['CD1_2'+'%s' %ukey], hwcs['CD2_2'+'%s' %ukey]))
+        norient = np.rad2deg(np.arctan2(hwcs['CD1_2' + '%s' % ukey], hwcs['CD2_2' + '%s' % ukey]))
         fobj[toextension].header['ORIENTAT'] = norient
     # Reset 2014 TDD keywords prior to computing new values (if any are computed)
-    for kw in ['TDD_CYA','TDD_CYB','TDD_CXA','TDD_CXB']:
+    for kw in ['TDD_CYA', 'TDD_CYB', 'TDD_CXA', 'TDD_CXB']:
         if kw in fobj[toextension].header:
             fobj[toextension].header[kw] = 0.0
 
-#header operations
+ 
+# header operations
+
+
 def _check_headerpars(fobj, ext):
     if not isinstance(fobj, fits.Header) and not isinstance(fobj, fits.HDUList) \
-                   and not isinstance(fobj, str):
+            and not isinstance(fobj, str):
         raise ValueError("Expected a file name, a file object or a header\n")
 
     if not isinstance(fobj, fits.Header):
-        #raise ValueError("Expected a valid ext parameter when input is a file")
         if not isinstance(ext, int) and not isinstance(ext, tuple):
             raise ValueError("Expected ext to be a number or a tuple, e.g. ('SCI', 1)\n")
 
+
 def _getheader(fobj, ext):
     if isinstance(fobj, str):
-        hdr = fits.getheader(fobj,ext)
+        hdr = fits.getheader(fobj, ext)
     elif isinstance(fobj, fits.Header):
         hdr = fobj
     else:
         hdr = fobj[ext].header
     return hdr
 
-def readAltWCS(fobj, ext, wcskey=' ',verbose=False):
+
+def readAltWCS(fobj, ext, wcskey=' ', verbose=False):
     """
     Reads in alternate primary WCS from specified extension.
 
@@ -495,12 +502,12 @@ def readAltWCS(fobj, ext, wcskey=' ',verbose=False):
     if isinstance(fobj, str):
         fobj = fits.open(fobj)
 
-    hdr = _getheader(fobj,ext)
+    hdr = _getheader(fobj, ext)
     try:
         nwcs = pywcs.WCS(hdr, fobj=fobj, key=wcskey)
     except KeyError:
         if verbose:
-            print('readAltWCS: Could not read WCS with key %s' %wcskey)
+            print('readAltWCS: Could not read WCS with key %s' % wcskey)
             print('            Skipping %s[%s]' % (fobj.filename(), str(ext)))
         return None
     hwcs = nwcs.to_header()
@@ -510,7 +517,8 @@ def readAltWCS(fobj, ext, wcskey=' ',verbose=False):
 
     return hwcs
 
-def convertAltWCS(fobj,ext,oldkey=" ",newkey=' '):
+
+def convertAltWCS(fobj, ext, oldkey=" ", newkey=' '):
     """
     Translates the alternate/primary WCS with one key to an alternate/primary WCS with
     another key.
@@ -534,7 +542,7 @@ def convertAltWCS(fobj,ext,oldkey=" ",newkey=' '):
     hdr: `astropy.io.fits.Header`
         header object with keywords renamed from oldkey to newkey
     """
-    hdr = readAltWCS(fobj,ext,wcskey=oldkey)
+    hdr = readAltWCS(fobj, ext, wcskey=oldkey)
     if hdr is None:
         return None
     # Converting WCS to new key
@@ -543,10 +551,11 @@ def convertAltWCS(fobj,ext,oldkey=" ",newkey=' '):
             cname = card
         else:
             cname = card.rstrip(oldkey)
-        hdr.rename_key(card,cname+newkey,force=True)
+        hdr.rename_key(card, cname + newkey, force=True)
 
     return hdr
 
+
 def wcskeys(fobj, ext=None):
     """
     Returns a list of characters used in the header for alternate
@@ -565,11 +574,12 @@ def wcskeys(fobj, ext=None):
     names = hdr["WCSNAME*"]
     d = []
     for key in names:
-        wkey = key.replace('WCSNAME','')
+        wkey = key.replace('WCSNAME', '')
         if wkey == '': wkey = ' '
         d.append(wkey)
     return d
 
+
 def wcsnames(fobj, ext=None):
     """
     Returns a dictionary of wcskey: WCSNAME pairs
@@ -588,11 +598,12 @@ def wcsnames(fobj, ext=None):
     names = hdr["WCSNAME*"]
     d = {}
     for keyword, value in names.items():
-        wkey = keyword.replace('WCSNAME','')
+        wkey = keyword.replace('WCSNAME', '')
         if wkey == '': wkey = ' '
         d[wkey] = value
     return d
 
+
 def available_wcskeys(fobj, ext=None):
     """
     Returns a list of characters which are not used in the header
@@ -618,6 +629,7 @@ def available_wcskeys(fobj, ext=None):
     [all_keys.remove(key) for key in used_keys]
     return all_keys
 
+
 def next_wcskey(fobj, ext=None):
     """
     Returns next available character to be used for an alternate WCS
@@ -638,6 +650,7 @@ def next_wcskey(fobj, ext=None):
     else:
         return None
 
+
 def getKeyFromName(header, wcsname):
     """
     If WCSNAME is found in header, return its key, else return
@@ -663,6 +676,7 @@ def getKeyFromName(header, wcsname):
         wkey = None
     return wkey
 
+
 def pc2cd(hdr, key=' '):
     """
     Convert a CD matrix to a CD matrix.
@@ -690,6 +704,7 @@ def pc2cd(hdr, key=' '):
         hdr['CD{0}{1}'.format(c, key)] = val
     return hdr
 
+
 def _parpasscheck(fobj, ext, wcskey, fromext=None, toext=None, reusekey=False):
     """
     Check input parameters to altwcs functions
@@ -722,7 +737,7 @@ def _parpasscheck(fobj, ext, wcskey, fromext=None, toext=None, reusekey=False):
             return False
 
     if not isinstance(ext, int) and not isinstance(ext, tuple) \
-        and not isinstance(ext,str) \
+        and not isinstance(ext, str) \
         and not isinstance(ext, list) and ext is not None:
         print("Ext must be integer, tuple, string,a list of int extension numbers, \n\
         or a list of tuples representing a fits extension, for example ('sci', 1).")
@@ -733,7 +748,7 @@ def _parpasscheck(fobj, ext, wcskey, fromext=None, toext=None, reusekey=False):
         return False
 
     if not isinstance(toext, list) and not isinstance(toext, str) and \
-                     toext is not None :
+                        toext is not None:
         print("toext must be a string or a list of strings representing extname")
         return False
 
@@ -743,6 +758,7 @@ def _parpasscheck(fobj, ext, wcskey, fromext=None, toext=None, reusekey=False):
 
     return True
 
+
 def closefobj(fname, f):
     """
     Functions in this module accept as input a file name or a file object.
@@ -752,6 +768,7 @@ def closefobj(fname, f):
     if isinstance(fname, str):
         f.close()
 
+
 def mapFitsExt2HDUListInd(fname, extname):
     """
     Map FITS extensions with 'EXTNAME' to HDUList indexes.
diff --git a/stwcs/wcsutil/convertwcs.py b/stwcs/wcsutil/convertwcs.py
index a384eb1..e47a829 100644
--- a/stwcs/wcsutil/convertwcs.py
+++ b/stwcs/wcsutil/convertwcs.py
@@ -1,4 +1,5 @@
-from __future__ import print_function
+from __future__ import absolute_import, division, print_function
+from astropy.io import fits
 try:
     import stwcs
     from stwcs import wcsutil
@@ -7,12 +8,12 @@ except:
 
 from stsci.tools import fileutil
 
-OPUS_WCSKEYS = ['OCRVAL1','OCRVAL2','OCRPIX1','OCRPIX2',
-                'OCD1_1','OCD1_2','OCD2_1','OCD2_2',
-                'OCTYPE1','OCTYPE2']
+OPUS_WCSKEYS = ['OCRVAL1', 'OCRVAL2', 'OCRPIX1', 'OCRPIX2',
+                'OCD1_1', 'OCD1_2', 'OCD2_1', 'OCD2_2',
+                'OCTYPE1', 'OCTYPE2']
 
 
-def archive_prefix_OPUS_WCS(fobj,extname='SCI'):
+def archive_prefix_OPUS_WCS(fobj, extname='SCI'):
     """ Identifies WCS keywords which were generated by OPUS and archived
         using a prefix of 'O' for all 'SCI' extensions in the file
 
@@ -28,43 +29,42 @@ def archive_prefix_OPUS_WCS(fobj,extname='SCI'):
         print('=====================')
         raise ImportError
 
-
     closefits = False
-    if isinstance(fobj,str):
+    if isinstance(fobj, str):
         # A filename was provided as input
-        fobj = fits.open(fobj,mode='update')
-        closefits=True
+        fobj = fits.open(fobj, mode='update')
+        closefits = True
 
     # Define the header
-    ext = ('sci',1)
+    ext = ('sci', 1)
     hdr = fobj[ext].header
 
     numextn = fileutil.countExtn(fobj)
     extlist = []
-    for e in range(1,numextn+1):
-        extlist.append(('sci',e))
+    for e in range(1, numextn + 1):
+        extlist.append(('sci', e))
 
     # Insure that the 'O' alternate WCS is present
     if 'O' not in wcsutil.wcskeys(hdr):
         # if not, archive the Primary WCS as the default OPUS WCS
-        wcsutil.archiveWCS(fobj,extlist, wcskey='O', wcsname='OPUS')
+        wcsutil.archiveWCS(fobj, extlist, wcskey='O', wcsname='OPUS')
 
     # find out how many SCI extensions are in the image
-    numextn = fileutil.countExtn(fobj,extname=extname)
+    numextn = fileutil.countExtn(fobj, extname=extname)
     if numextn == 0:
         extname = 'PRIMARY'
 
     # create HSTWCS object from PRIMARY WCS
-    wcsobj = wcsutil.HSTWCS(fobj,ext=ext,wcskey='O')
+    wcsobj = wcsutil.HSTWCS(fobj, ext=ext, wcskey='O')
     # get list of WCS keywords
     wcskeys = list(wcsobj.wcs2header().keys())
 
     # For each SCI extension...
-    for e in range(1,numextn+1):
+    for e in range(1, numextn + 1):
         # Now, look for any WCS keywords with a prefix of 'O'
         for key in wcskeys:
-            okey = 'O'+key[:7]
-            hdr = fobj[(extname,e)].header
+            okey = 'O' + key[: 7]
+            hdr = fobj[(extname, e)].header
             if okey in hdr:
                 # Update alternate WCS keyword with prefix-O OPUS keyword value
                 hdr[key] = hdr[okey]
@@ -72,7 +72,8 @@ def archive_prefix_OPUS_WCS(fobj,extname='SCI'):
     if closefits:
         fobj.close()
 
-def create_prefix_OPUS_WCS(fobj,extname='SCI'):
+
+def create_prefix_OPUS_WCS(fobj, extname='SCI'):
     """ Creates alternate WCS with a prefix of 'O' for OPUS generated WCS values
         to work with old MultiDrizzle.
 
@@ -91,10 +92,10 @@ def create_prefix_OPUS_WCS(fobj,extname='SCI'):
     owcskeys = OPUS_WCSKEYS
 
     closefits = False
-    if isinstance(fobj,str):
+    if isinstance(fobj, str):
         # A filename was provided as input
         fobj = fits.open(fobj, mode='update')
-        closefits=True
+        closefits = True
     else:
         # check to make sure this FITS obj has been opened in update mode
         if fobj.fileinfo(0)['filemode'] != 'update':
@@ -102,16 +103,16 @@ def create_prefix_OPUS_WCS(fobj,extname='SCI'):
             raise IOError
 
     # check for existance of O-prefix WCS
-    if owcskeys[0] not in fobj['sci',1].header:
+    if owcskeys[0] not in fobj['sci', 1].header:
 
         # find out how many SCI extensions are in the image
-        numextn = fileutil.countExtn(fobj,extname=extname)
+        numextn = fileutil.countExtn(fobj, extname=extname)
         if numextn == 0:
             extname = ''
-        for extn in range(1,numextn+1):
-            hdr = fobj[(extname,extn)].header
+        for extn in range(1, numextn + 1):
+            hdr = fobj[(extname, extn)].header
             for okey in owcskeys:
-                hdr[okey] = hdr[okey[1:]+'O']
+                hdr[okey] = hdr[okey[1: ] + 'O']
 
     # Close FITS image if we had to open it...
     if closefits:
diff --git a/stwcs/wcsutil/getinput.py b/stwcs/wcsutil/getinput.py
index 8ee1123..c8b3b1b 100644
--- a/stwcs/wcsutil/getinput.py
+++ b/stwcs/wcsutil/getinput.py
@@ -1,23 +1,27 @@
+from __future__ import absolute_import, division, print_function
+
 from astropy.io import fits
 from stsci.tools import irafglob, fileutil, parseinput
+#from . import HSTWCS
+
 
 def parseSingleInput(f=None, ext=None):
     if isinstance(f, str):
         # create an HSTWCS object from a filename
-        if ext != None:
+        if ext is not None:
             filename = f
-            if isinstance(ext,tuple):
+            if isinstance(ext, tuple):
                 if ext[0] == '':
-                    extnum = ext[1] # handle ext=('',1)
+                    extnum = ext[1]  # handle ext=('',1)
                 else:
                     extnum = ext
             else:
                 extnum = int(ext)
-        elif ext == None:
+        elif ext is None:
             filename, ext = fileutil.parseFilename(f)
             ext = fileutil.parseExtn(ext)
             if ext[0] == '':
-                extnum = int(ext[1]) #handle ext=('',extnum)
+                extnum = int(ext[1])  # handle ext=('',extnum)
             else:
                 extnum = ext
         phdu = fits.open(filename)
@@ -29,7 +33,7 @@ def parseSingleInput(f=None, ext=None):
 
     elif isinstance(f, fits.HDUList):
         phdu = f
-        if ext == None:
+        if ext is None:
             extnum = 0
         else:
             extnum = ext
@@ -54,9 +58,9 @@ def parseMultipleInput(input):
                 filelist, output = parseinput.parseinput(input)
             except IOError: raise
     elif isinstance(input, list):
-        if isinstance(input[0], wcsutil.HSTWCS):
-            # a list of HSTWCS objects
-            return input
-        else:
-            filelist = input[:]
+        #if isinstance(input[0], HSTWCS):
+            ## a list of HSTWCS objects
+            #return input
+        #else:
+        filelist = input[:]
     return filelist
diff --git a/stwcs/wcsutil/headerlet.py b/stwcs/wcsutil/headerlet.py
index 5a980aa..03861df 100644
--- a/stwcs/wcsutil/headerlet.py
+++ b/stwcs/wcsutil/headerlet.py
@@ -34,7 +34,9 @@ from . import wcscorr
 from .hstwcs import HSTWCS
 from .mappings import basic_wcs
 
-#### Logging support functions
+# Logging support functions
+
+
 class FuncNameLoggingFormatter(logging.Formatter):
     def __init__(self, fmt=None, datefmt=None):
         if '%(funcName)s' not in fmt:
@@ -59,8 +61,8 @@ logger.addHandler(ch)
 logger.setLevel(logging.DEBUG)
 
 FITS_STD_KW = ['XTENSION', 'BITPIX', 'NAXIS', 'PCOUNT',
-             'GCOUNT', 'EXTNAME', 'EXTVER', 'ORIGIN',
-             'INHERIT', 'DATE', 'IRAF-TLM']
+               'GCOUNT', 'EXTNAME', 'EXTVER', 'ORIGIN',
+               'INHERIT', 'DATE', 'IRAF-TLM']
 
 DEFAULT_SUMMARY_COLS = ['HDRNAME', 'WCSNAME', 'DISTNAME', 'AUTHOR', 'DATE',
                         'SIPNAME', 'NPOLFILE', 'D2IMFILE', 'DESCRIP']
@@ -120,10 +122,13 @@ def with_logging(func):
         return func(*args, **kw)
     return wrapped
 
-#### Utility functions
+# Utility functions
+
+
 def is_par_blank(par):
     return par in ['', ' ', 'INDEF', "None", None]
 
+
 def parse_filename(fname, mode='readonly'):
     """
     Interprets the input as either a filename of a file that needs to be opened
@@ -174,6 +179,7 @@ def parse_filename(fname, mode='readonly'):
             fname = ''
     return fobj, fname, close_fobj
 
+
 def get_headerlet_kw_names(fobj, kw='HDRNAME'):
     """
     Returns a list of specified keywords from all HeaderletHDU
@@ -198,6 +204,7 @@ def get_headerlet_kw_names(fobj, kw='HDRNAME'):
 
     return hdrnames
 
+
 def get_header_kw_vals(hdr, kwname, kwval, default=0):
     if kwval is None:
         if kwname in hdr:
@@ -206,6 +213,7 @@ def get_header_kw_vals(hdr, kwname, kwval, default=0):
             kwval = default
     return kwval
 
+
 @with_logging
 def find_headerlet_HDUs(fobj, hdrext=None, hdrname=None, distname=None,
                         strict=True, logging=False, logmode='w'):
@@ -259,9 +267,9 @@ def find_headerlet_HDUs(fobj, hdrext=None, hdrname=None, distname=None,
 
     hdrlets = []
     if hdrext is not None and isinstance(hdrext, int):
-        if hdrext in range(len(fobj)): # insure specified hdrext is in fobj
+        if hdrext in range(len(fobj)):  # insure specified hdrext is in fobj
             if isinstance(fobj[hdrext], fits.hdu.base.NonstandardExtHDU) and \
-                fobj[hdrext].header['EXTNAME'] == 'HDRLET':
+                    fobj[hdrext].header['EXTNAME'] == 'HDRLET':
                 hdrlets.append(hdrext)
     else:
         for ext in fobj:
@@ -280,9 +288,9 @@ def find_headerlet_HDUs(fobj, hdrext=None, hdrname=None, distname=None,
                                     (hdrextnum == ext.header['EXTVER']) and
                                     (hdrextname == ext.header['EXTNAME']))
                     hdrname_match = ((hdrname is not None) and
-                                        (hdrname == ext.header['HDRNAME']))
+                                     (hdrname == ext.header['HDRNAME']))
                     distname_match = ((distname is not None) and
-                                        (distname == ext.header['DISTNAME']))
+                                      (distname == ext.header['DISTNAME']))
                     if hdrext_match or hdrname_match or distname_match:
                         hdrlets.append(fobj.index(ext))
 
@@ -310,6 +318,7 @@ def find_headerlet_HDUs(fobj, hdrext=None, hdrname=None, distname=None,
 
     return hdrlets
 
+
 def verify_hdrname_is_unique(fobj, hdrname):
     """
     Verifies that no other HeaderletHDU extension has the specified hdrname.
@@ -331,6 +340,7 @@ def verify_hdrname_is_unique(fobj, hdrname):
 
     return unique
 
+
 def update_versions(sourcehdr, desthdr):
     """
     Update keywords which store version numbers
@@ -344,6 +354,7 @@ def update_versions(sourcehdr, desthdr):
         except KeyError:
             desthdr[key] = (" ", phdukw[key])
 
+
 def update_ref_files(source, dest):
     """
     Update the reference files name in the primary header of 'dest'
@@ -372,8 +383,9 @@ def update_ref_files(source, dest):
             phdukw[key] = False
     return phdukw
 
+
 def print_summary(summary_cols, summary_dict, pad=2, maxwidth=None, idcol=None,
-                    output=None, clobber=True, quiet=False ):
+                  output=None, clobber=True, quiet=False ):
     """
     Print out summary dictionary to STDOUT, and possibly an output file
 
@@ -404,9 +416,9 @@ def print_summary(summary_cols, summary_dict, pad=2, maxwidth=None, idcol=None,
     for row in range(nrows):
         if idcol:
             outstr += COLUMN_FMT.format(idcol['vals'][row],
-                                        width=idcol['width']+pad)
+                                        width=idcol['width'] + pad)
         for kw in summary_cols:
-            val = summary_dict[kw]['vals'][row][:(column_widths[kw]-pad)]
+            val = summary_dict[kw]['vals'][row][:(column_widths[kw] - pad)]
             outstr += COLUMN_FMT.format(val, width=column_widths[kw])
         outstr += '\n'
     if not quiet:
@@ -415,7 +427,7 @@ def print_summary(summary_cols, summary_dict, pad=2, maxwidth=None, idcol=None,
     # If specified, write info to separate text file
     write_file = False
     if output:
-        output = fu.osfn(output) # Expand any environment variables in filename
+        output = fu.osfn(output)  # Expand any environment variables in filename
         write_file = True
         if os.path.exists(output):
             if clobber:
@@ -430,11 +442,13 @@ def print_summary(summary_cols, summary_dict, pad=2, maxwidth=None, idcol=None,
             fout.write(outstr)
             fout.close()
 
-#### Private utility functions
+# Private utility functions
+
+
 def _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
-                            sipname, npolfile, d2imfile,
-                            nmatch,catalog, wcskey,
-                            author, descrip, history):
+                        sipname, npolfile, d2imfile,
+                        nmatch, catalog, wcskey,
+                        author, descrip, history):
     # convert input values into valid FITS kw values
     if author is None:
         author = ''
@@ -447,7 +461,7 @@ def _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
     npolname, npolfile = utils.build_npolname(fobj, npolfile)
     logger.info("Setting npolfile value to %s" % npolname)
 
-    d2imname, d2imfile = utils.build_d2imname(fobj,d2imfile)
+    d2imname, d2imfile = utils.build_d2imname(fobj, d2imfile)
     logger.info("Setting d2imfile value to %s" % d2imname)
 
     distname = utils.build_distname(sipname, npolname, d2imname)
@@ -461,23 +475,14 @@ def _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
     else:
         history = ''
 
-    rms_ra = fobj[wcsext].header.get("CRDER1"+wcskey, 0)
-    rms_dec = fobj[wcsext].header.get("CRDER2"+wcskey, 0)
+    rms_ra = fobj[wcsext].header.get("CRDER1" + wcskey, 0)
+    rms_dec = fobj[wcsext].header.get("CRDER2" + wcskey, 0)
     if not nmatch:
-        nmatch = fobj[wcsext].header.get("NMATCH"+wcskey, 0)
+        nmatch = fobj[wcsext].header.get("NMATCH" + wcskey, 0)
     if not catalog:
-        catalog = fobj[wcsext].header.get('CATALOG'+wcskey, "")
+        catalog = fobj[wcsext].header.get('CATALOG' + wcskey, "")
     # get the version of STWCS used to create the WCS of the science file.
-    #try:
-        #upwcsver = fobj[0].header.cards[fobj[0].header.index('UPWCSVER')]
-    #except KeyError:
-        #upwcsver = pyfits.Card("UPWCSVER", " ",
-                               #"Version of STWCS used to update the WCS")
-    #try:
-        #pywcsver = fobj[0].header.cards[fobj[0].header.index('PYWCSVER')]
-    #except KeyError:
-        #pywcsver = pyfits.Card("PYWCSVER", " ",
-                               #"Version of PYWCS used to update the WCS")
+
     upwcsver = fobj[0].header.get('UPWCSVER', "")
     pywcsver = fobj[0].header.get('PYWCSVER', "")
     # build Primary HDU
@@ -495,7 +500,7 @@ def _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
     phdu.header['D2IMFILE'] = (d2imfile,
                                'origin of detector to image correction')
     phdu.header['IDCTAB'] = (idctab,
-                               'origin of Polynomial Distortion')
+                             'origin of Polynomial Distortion')
     phdu.header['AUTHOR'] = (author, 'headerlet created by this user')
     phdu.header['DESCRIP'] = (descrip,
                               'Short description of headerlet solution')
@@ -526,7 +531,9 @@ def _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
     return phdu
 
 
-#### Public Interface functions
+# Public Interface functions
+
+
 @with_logging
 def extract_headerlet(filename, output, extnum=None, hdrname=None,
                       clobber=False, logging=True):
@@ -611,11 +618,11 @@ def extract_headerlet(filename, output, extnum=None, hdrname=None,
 
 @with_logging
 def write_headerlet(filename, hdrname, output=None, sciext='SCI',
-                        wcsname=None, wcskey=None, destim=None,
-                        sipname=None, npolfile=None, d2imfile=None,
-                        author=None, descrip=None, history=None,
-                        nmatch=None, catalog=None,
-                        attach=True, clobber=False, logging=False):
+                    wcsname=None, wcskey=None, destim=None,
+                    sipname=None, npolfile=None, d2imfile=None,
+                    author=None, descrip=None, history=None,
+                    nmatch=None, catalog=None,
+                    attach=True, clobber=False, logging=False):
 
     """
     Save a WCS as a headerlet FITS file.
@@ -733,22 +740,22 @@ def write_headerlet(filename, hdrname, output=None, sciext='SCI',
 
         # Interpret sciext input for this file
         if isinstance(sciext, int):
-            sciextlist = [sciext] # allow for specification of simple FITS header
+            sciextlist = [sciext]  # allow for specification of simple FITS header
         elif isinstance(sciext, str):
             numsciext = countExtn(fobj, sciext)
             if numsciext > 0:
-                sciextlist = [tuple((sciext,i)) for i in range(1, numsciext+1)]
+                sciextlist = [tuple((sciext, i)) for i in range(1, numsciext + 1)]
             else:
                 sciextlist = [0]
         elif isinstance(sciext, list):
             sciextlist = sciext
         else:
-            errstr = "Expected sciext to be a list of FITS extensions with science data\n"+\
-                  "    a valid EXTNAME string, or an integer."
+            errstr = "Expected sciext to be a list of FITS extensions with science data\n" + \
+                "    a valid EXTNAME string, or an integer."
             logger.critical(errstr)
             raise ValueError
 
-        wnames = altwcs.wcsnames(fobj,ext=sciextlist[0])
+        wnames = altwcs.wcsnames(fobj, ext=sciextlist[0])
 
         # Insure that WCSCORR table has been created with all original
         # WCS's recorded prior to adding the headerlet WCS
@@ -756,7 +763,7 @@ def write_headerlet(filename, hdrname, output=None, sciext='SCI',
 
         if wcsname is None:
             scihdr = fobj[sciextlist[0]].header
-            wname = scihdr['wcsname'+wcskey]
+            wname = scihdr['wcsname' + wcskey]
         else:
             wname = wcsname
         if hdrname in [None, ' ', '']:
@@ -764,17 +771,17 @@ def write_headerlet(filename, hdrname, output=None, sciext='SCI',
 
         logger.critical('Creating the headerlet from image %s' % fname)
         hdrletobj = create_headerlet(fobj, sciext=sciextlist,
-                                    wcsname=wname, wcskey=wcskey,
-                                    hdrname=hdrname,
-                                    sipname=sipname, npolfile=npolfile,
-                                    d2imfile=d2imfile, author=author,
-                                    descrip=descrip, history=history,
-                                    nmatch=nmatch, catalog=catalog,
-                                    logging=False)
+                                     wcsname=wname, wcskey=wcskey,
+                                     hdrname=hdrname,
+                                     sipname=sipname, npolfile=npolfile,
+                                     d2imfile=d2imfile, author=author,
+                                     descrip=descrip, history=history,
+                                     nmatch=nmatch, catalog=catalog,
+                                     logging=False)
 
         if attach:
             # Check to see whether or not a HeaderletHDU with
-            #this hdrname already exists
+            # this hdrname already exists
             hdrnames = get_headerlet_kw_names(fobj)
             if hdrname not in hdrnames:
                 hdrlet_hdu = HeaderletHDU.fromheaderlet(hdrletobj)
@@ -810,14 +817,15 @@ def write_headerlet(filename, hdrname, output=None, sciext='SCI',
             outname = output
 
         if not outname.endswith('.fits'):
-            outname = '{0}_{1}_hlet.fits'.format(frootname,outname)
+            outname = '{0}_{1}_hlet.fits'.format(frootname, outname)
 
         # If user specifies an output filename for headerlet, write it out
         hdrletobj.tofile(outname, clobber=clobber)
-        logger.critical( 'Created Headerlet file %s ' % outname)
+        logger.critical('Created Headerlet file %s ' % outname)
 
         del hdrletobj
 
+
 @with_logging
 def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
                      wcskey=" ", wcsname=None,
@@ -856,7 +864,8 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
             if " ", use the primary (default)
             if None use wcsname
     wcsname: string or None
-            if wcskey is None use wcsname specified here to choose an alternate WCS for the headerlet
+            if wcskey is None use wcsname specified here to choose an alternate WCS
+            for the headerlet
     sipname: string or None (default)
             Name of unique file where the polynomial distortion coefficients were
             read from. If None, the behavior is:
@@ -935,7 +944,7 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
     if not wcsname:
         # User did not specify a value for 'wcsname'
         if wcsnamekw in fobj[wcsext].header:
-            #check if there's a WCSNAME for this wcskey in the header
+            # check if there's a WCSNAME for this wcskey in the header
             wcsname = fobj[wcsext].header[wcsnamekw]
             logger.info("Setting wcsname from header[%s] to %s" % (wcsnamekw, wcsname))
         else:
@@ -973,8 +982,9 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
     wkeys = altwcs.wcskeys(fobj, ext=wcsext)
     if wcskey != ' ':
         if wcskey not in wkeys:
-            logger.critical('No WCS with wcskey=%s found in extension %s.  Skipping...' % (wcskey, str(wcsext)))
-            raise ValueError("No WCS with wcskey=%s found in extension %s.  Skipping...' % (wcskey, str(wcsext))")
+            mess = "Skipping extension {0} - no WCS with wcskey={1} found.".format(wcsext, wcskey)
+            logger.critical(mess)
+            raise ValueError(mess)
 
     # get remaining required keywords
     if destim is None:
@@ -1005,13 +1015,11 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
                 logger.critical(message)
                 raise KeyError
 
-
-
     hdul = []
     phdu = _create_primary_HDU(fobj, fname, wcsext, destim, hdrname, wcsname,
-                             sipname, npolfile, d2imfile,
-                             nmatch, catalog, wcskey,
-                             author, descrip, history)
+                               sipname, npolfile, d2imfile,
+                               nmatch, catalog, wcskey,
+                               author, descrip, history)
     hdul.append(phdu)
     wcsdvarr_extns = []
     """
@@ -1100,14 +1108,6 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
             whdu.update_ext_version(ihdu.header['D2IM2.EXTVER'])
             hdul.append(whdu)
 
-
-        #if hwcs.det2im1 or hwcs.det2im2:
-            #try:
-                #darr = hdul[('D2IMARR', 1)]
-            #except KeyError:
-                #whdu = whdul[('D2IMARR')]
-                #whdu.update_ext_version(1)
-                #hdul.append(whdu)
     if close_file:
         fobj.close()
 
@@ -1115,9 +1115,10 @@ def create_headerlet(filename, sciext='SCI', hdrname=None, destim=None,
     hlet.init_attrs()
     return hlet
 
+
 @with_logging
 def apply_headerlet_as_primary(filename, hdrlet, attach=True, archive=True,
-                                force=False, logging=False, logmode='a'):
+                               force=False, logging=False, logmode='a'):
     """
     Apply headerlet 'hdrfile' to a science observation 'destfile' as the primary WCS
 
@@ -1146,18 +1147,19 @@ def apply_headerlet_as_primary(filename, hdrlet, attach=True, archive=True,
         hdrlet = [hdrlet]
     if len(hdrlet) != len(filename):
         logger.critical("Filenames must have matching headerlets. "
-                "{0:d} filenames and {1:d} headerlets specified".format(len(filename),len(hdrlet)))
+                        "{0:d} filenames and {1:d} headerlets specified".format(len(filename),
+                                                                                len(hdrlet)))
 
-    for fname,h in zip(filename,hdrlet):
-        print("Applying {0} as Primary WCS to {1}".format(h,fname))
+    for fname, h in zip(filename, hdrlet):
+        print("Applying {0} as Primary WCS to {1}".format(h, fname))
         hlet = Headerlet.fromfile(h, logging=logging, logmode=logmode)
         hlet.apply_as_primary(fname, attach=attach, archive=archive,
-                          force=force)
+                              force=force)
 
 
 @with_logging
 def apply_headerlet_as_alternate(filename, hdrlet, attach=True, wcskey=None,
-                                wcsname=None, logging=False, logmode='w'):
+                                 wcsname=None, logging=False, logmode='w'):
     """
     Apply headerlet to a science observation as an alternate WCS
 
@@ -1188,13 +1190,14 @@ def apply_headerlet_as_alternate(filename, hdrlet, attach=True, wcskey=None,
         hdrlet = [hdrlet]
     if len(hdrlet) != len(filename):
         logger.critical("Filenames must have matching headerlets. "
-                "{0:d} filenames and {1:d} headerlets specified".format(len(filename),len(hdrlet)))
+                        "{0:d} filenames and {1:d} headerlets specified".format(len(filename),
+                                                                                len(hdrlet)))
 
-    for fname,h in zip(filename,hdrlet):
-        print('Applying {0} as an alternate WCS to {1}'.format(h,fname))
+    for fname, h in zip(filename, hdrlet):
+        print('Applying {0} as an alternate WCS to {1}'.format(h, fname))
         hlet = Headerlet.fromfile(h, logging=logging, logmode=logmode)
         hlet.apply_as_alternate(fname, attach=attach,
-                            wcsname=wcsname, wcskey=wcskey)
+                                wcsname=wcsname, wcskey=wcskey)
 
 
 @with_logging
@@ -1218,12 +1221,13 @@ def attach_headerlet(filename, hdrlet, logging=False, logmode='a'):
         hdrlet = [hdrlet]
     if len(hdrlet) != len(filename):
         logger.critical("Filenames must have matching headerlets. "
-                "{0:d} filenames and {1:d} headerlets specified".format(len(filename),len(hdrlet)))
+                        "{0:d} filenames and {1:d} headerlets specified".format(len(filename),
+                                                                                len(hdrlet)))
 
-    for fname,h in zip(filename,hdrlet):
-        print('Attaching {0} as Headerlet extension to {1}'.format(h,fname))
+    for fname, h in zip(filename, hdrlet):
+        print('Attaching {0} as Headerlet extension to {1}'.format(h, fname))
         hlet = Headerlet.fromfile(h, logging=logging, logmode=logmode)
-        hlet.attach_to_file(fname,archive=True)
+        hlet.attach_to_file(fname, archive=True)
 
 
 @with_logging
@@ -1262,12 +1266,13 @@ def delete_headerlet(filename, hdrname=None, hdrext=None, distname=None,
         filename = [filename]
 
     for f in filename:
-        print("Deleting Headerlet from ",f)
+        print("Deleting Headerlet from ", f)
         _delete_single_headerlet(f, hdrname=hdrname, hdrext=hdrext,
-                            distname=distname, logging=logging, logmode='a')
+                                 distname=distname, logging=logging, logmode='a')
+
 
 def _delete_single_headerlet(filename, hdrname=None, hdrext=None, distname=None,
-                     logging=False, logmode='w'):
+                             logging=False, logmode='w'):
     """
     Deletes HeaderletHDU(s) from a SINGLE science file
 
@@ -1297,7 +1302,7 @@ def _delete_single_headerlet(filename, hdrname=None, hdrext=None, distname=None,
     logmode: 'a' or 'w'
     """
     hdrlet_ind = find_headerlet_HDUs(filename, hdrname=hdrname, hdrext=hdrext,
-                            distname=distname, logging=logging, logmode='a')
+                                     distname=distname, logging=logging, logmode='a')
     if len(hdrlet_ind) == 0:
         message = """
         No HDUs deleted... No Headerlet HDUs found with '
@@ -1404,8 +1409,8 @@ def headerlet_summary(filename, columns=None, pad=2, maxwidth=None,
 
     # Print out the summary dictionary
     print_summary(summary_cols, summary_dict, pad=pad, maxwidth=maxwidth,
-                    idcol=extnums_col, output=output,
-                    clobber=clobber, quiet=quiet)
+                  idcol=extnums_col, output=output,
+                  clobber=clobber, quiet=quiet)
 
 
 @with_logging
@@ -1452,7 +1457,7 @@ def restore_from_headerlet(filename, hdrname=None, hdrext=None, archive=True,
         message = """
         Multiple Headerlet extensions found with the same name.
         %d Headerlets with "%s" = %s found in %s.
-        """% (len(hdrlet_ind), kwerr, kwval, fname)
+        """ % (len(hdrlet_ind), kwerr, kwval, fname)
         if close_fobj:
             fobj.close()
         logger.critical(message)
@@ -1464,7 +1469,7 @@ def restore_from_headerlet(filename, hdrname=None, hdrext=None, archive=True,
     if hasattr(fobj[hdrlet_ind[0]], 'hdulist'):
         hdrlet = fobj[hdrlet_indx].hdulist
     else:
-        hdrlet = fobj[hdrlet_indx].headerlet # older convention in PyFITS
+        hdrlet = fobj[hdrlet_indx].headerlet  # older convention in PyFITS
 
     # read in the names of the extensions which HeaderletHDU updates
     extlist = []
@@ -1503,7 +1508,7 @@ def restore_from_headerlet(filename, hdrname=None, hdrext=None, archive=True,
         else:
             if 'idctab' in scihdr:
                 priwcs_hdrname = ''.join(['IDC_',
-                        utils.extract_rootname(scihdr['idctab'], suffix='_idc')])
+                                          utils.extract_rootname(scihdr['idctab'], suffix='_idc')])
             else:
                 priwcs_hdrname = 'UNKNOWN'
             priwcs_name = priwcs_hdrname
@@ -1513,7 +1518,7 @@ def restore_from_headerlet(filename, hdrname=None, hdrext=None, archive=True,
     if archive and priwcs_unique:
         if priwcs_unique:
             newhdrlet = create_headerlet(fobj, sciext=scihdr['extname'],
-                        hdrname=priwcs_hdrname)
+                                         hdrname=priwcs_hdrname)
             newhdrlet.attach_to_file(fobj)
     #
     # copy hdrlet as a primary
@@ -1598,7 +1603,7 @@ def restore_all_with_distname(filename, distname, primary, archive=True,
     if hasattr(fobj[primary_ind], 'hdulist'):
         primary_hdrlet = fobj[primary_ind].hdulist
     else:
-        primary_hdrlet = fobj[primary_ind].headerlet # older convention in PyFITS
+        primary_hdrlet = fobj[primary_ind].headerlet  # older convention in PyFITS
     pri_distname = primary_hdrlet[0].header['distname']
     if pri_distname != distname:
         if close_fobj:
@@ -1625,7 +1630,7 @@ def restore_all_with_distname(filename, distname, primary, archive=True,
             if hasattr(fobj[hlet], 'hdulist'):
                 hdrlet = fobj[hlet].hdulist
             else:
-                hdrlet = fobj[hlet].headerlet # older convention in PyFITS
+                hdrlet = fobj[hlet].headerlet  # older convention in PyFITS
             if hlet == primary_ind:
                 hdrlet.apply_as_primary(fobj, attach=False,
                                         archive=archive, force=True)
@@ -1641,11 +1646,11 @@ def restore_all_with_distname(filename, distname, primary, archive=True,
 
 @with_logging
 def archive_as_headerlet(filename, hdrname, sciext='SCI',
-                        wcsname=None, wcskey=None, destim=None,
-                        sipname=None, npolfile=None, d2imfile=None,
-                        author=None, descrip=None, history=None,
-                        nmatch=None, catalog=None,
-                        logging=False, logmode='w'):
+                         wcsname=None, wcskey=None, destim=None,
+                         sipname=None, npolfile=None, d2imfile=None,
+                         author=None, descrip=None, history=None,
+                         nmatch=None, catalog=None,
+                         logging=False, logmode='w'):
     """
     Save a WCS as a headerlet extension and write it out to a file.
 
@@ -1735,7 +1740,7 @@ def archive_as_headerlet(filename, hdrname, sciext='SCI',
 
     if wcsname is None:
         scihdr = fobj[sciext, 1].header
-        wcsname = scihdr['wcsname'+wcskey]
+        wcsname = scihdr['wcsname' + wcskey]
 
     if hdrname in [None, ' ', '']:
         hdrname = wcsname
@@ -1745,13 +1750,13 @@ def archive_as_headerlet(filename, hdrname, sciext='SCI',
     hdrnames = get_headerlet_kw_names(fobj)
     if hdrname not in hdrnames:
         hdrletobj = create_headerlet(fobj, sciext=sciext,
-                                    wcsname=wcsname, wcskey=wcskey,
-                                    hdrname=hdrname,
-                                    sipname=sipname, npolfile=npolfile,
-                                    d2imfile=d2imfile, author=author,
-                                    descrip=descrip, history=history,
-                                    nmatch=nmatch, catalog=catalog,
-                                    logging=False)
+                                     wcsname=wcsname, wcskey=wcskey,
+                                     hdrname=hdrname,
+                                     sipname=sipname, npolfile=npolfile,
+                                     d2imfile=d2imfile, author=author,
+                                     descrip=descrip, history=history,
+                                     nmatch=nmatch, catalog=catalog,
+                                     logging=False)
         hlt_hdu = HeaderletHDU.fromheaderlet(hdrletobj)
 
         if destim is not None:
@@ -1771,7 +1776,10 @@ def archive_as_headerlet(filename, hdrname, sciext='SCI',
     if close_fobj:
         fobj.close()
 
-#### Headerlet Class definitions
+
+# Headerlet Class definitions
+
+
 class Headerlet(fits.HDUList):
     """
     A Headerlet class
@@ -1811,9 +1819,9 @@ class Headerlet(fits.HDUList):
         self.distname = self[0].header["DISTNAME"]
 
         try:
-            self.vafactor = self[("SIPWCS", 1)].header.get("VAFACTOR", 1) #None instead of 1?
+            self.vafactor = self[("SIPWCS", 1)].header.get("VAFACTOR", 1)  # None instead of 1?
         except (IndexError, KeyError):
-            self.vafactor = self[0].header.get("VAFACTOR", 1) #None instead of 1?
+            self.vafactor = self[0].header.get("VAFACTOR", 1)  # None instead of 1?
         self.author = self[0].header["AUTHOR"]
         self.descrip = self[0].header["DESCRIP"]
 
@@ -1846,7 +1854,7 @@ class Headerlet(fits.HDUList):
         init_logging('class Headerlet', level=logging, mode=logmode)
         return hlet
 
-    def  apply_as_primary(self, fobj, attach=True, archive=True, force=False):
+    def apply_as_primary(self, fobj, attach=True, archive=True, force=False):
         """
         Copy this headerlet as a primary WCS to fobj
 
@@ -1877,7 +1885,8 @@ class Headerlet(fits.HDUList):
             if close_dest:
                 fobj.close()
             raise ValueError("Destination name does not match headerlet"
-                "Observation %s cannot  be updated with headerlet %s" % (fname, self.hdrname))
+                             "Observation {0} cannot be updated with"
+                             "headerlet {1}".format((fname, self.hdrname)))
 
         # Check to see whether the distortion model in the destination
         # matches the distortion model in the headerlet being applied
@@ -1886,7 +1895,7 @@ class Headerlet(fits.HDUList):
         dist_models_equal = self.equal_distmodel(dname)
         if not dist_models_equal and not force:
             raise ValueError("Distortion models do not match"
-            " To overwrite the distortion model, set force=True")
+                             " To overwrite the distortion model, set force=True")
 
         orig_hlt_hdu = None
         numhlt = countExtn(fobj, 'HDRLET')
@@ -1896,15 +1905,14 @@ class Headerlet(fits.HDUList):
         # WCS's recorded prior to adding the headerlet WCS
         wcscorr.init_wcscorr(fobj)
 
-
-        ### start archive
+        # start archive
         # If archive has been specified
-        #   regardless of whether or not the distortion models are equal...
+        # regardless of whether or not the distortion models are equal...
 
         numsip = countExtn(self, 'SIPWCS')
         sciext_list = []
         alt_hlethdu = []
-        for i in range(1, numsip+1):
+        for i in range(1, numsip + 1):
             sipheader = self[('SIPWCS', i)].header
             sciext_list.append((sipheader['TG_ENAME'], sipheader['TG_EVER']))
         target_ext = sciext_list[0]
@@ -1920,10 +1928,10 @@ class Headerlet(fits.HDUList):
                 # Create a headerlet for the original Primary WCS data in the file,
                 # create an HDU from the original headerlet, and append it to
                 # the file
-                orig_hlt = create_headerlet(fobj, sciext=sciext_list, #[target_ext],
-                                wcsname=wcsname,
-                                hdrname=hdrname,
-                                logging=self.logging)
+                orig_hlt = create_headerlet(fobj, sciext=sciext_list,  # [target_ext],
+                                            wcsname=wcsname,
+                                            hdrname=hdrname,
+                                            logging=self.logging)
                 orig_hlt_hdu = HeaderletHDU.fromheaderlet(orig_hlt)
                 numhlt += 1
                 orig_hlt_hdu.header['EXTVER'] = numhlt
@@ -1931,7 +1939,6 @@ class Headerlet(fits.HDUList):
             else:
                 logger.info("Headerlet with name %s is already attached" % hdrname)
 
-
             if dist_models_equal:
                 # Use the WCSNAME to determine whether or not to archive
                 # Primary WCS as altwcs
@@ -1945,8 +1952,8 @@ class Headerlet(fits.HDUList):
                     else:
                         if 'idctab' in scihdr:
                             priwcs_name = ''.join(['IDC_',
-                                utils.extract_rootname(scihdr['idctab'],
-                                                        suffix='_idc')])
+                                                   utils.extract_rootname(scihdr['idctab'],
+                                                                          suffix='_idc')])
                         else:
                             priwcs_name = 'UNKNOWN'
                 nextkey = altwcs.next_wcskey(fobj, ext=target_ext)
@@ -1958,11 +1965,11 @@ class Headerlet(fits.HDUList):
                     if hname != 'OPUS' and hname not in hdrlet_extnames:
                         # get HeaderletHDU for alternate WCS as well
                         alt_hlet = create_headerlet(fobj, sciext=sciext_list,
-                                wcsname=hname, wcskey=wcskey,
-                                hdrname=hname, sipname=None,
-                                npolfile=None, d2imfile=None,
-                                author=None, descrip=None, history=None,
-                                logging=self.logging)
+                                                    wcsname=hname, wcskey=wcskey,
+                                                    hdrname=hname, sipname=None,
+                                                    npolfile=None, d2imfile=None,
+                                                    author=None, descrip=None, history=None,
+                                                    logging=self.logging)
                         numhlt += 1
                         alt_hlet_hdu = HeaderletHDU.fromheaderlet(alt_hlet)
                         alt_hlet_hdu.header['EXTVER'] = numhlt
@@ -1970,8 +1977,8 @@ class Headerlet(fits.HDUList):
                         hdrlet_extnames.append(hname)
 
         self._del_dest_WCS_ext(fobj)
-        for i in range(1, numsip+1):
-            target_ext = sciext_list[i-1]
+        for i in range(1, numsip + 1):
+            target_ext = sciext_list[i - 1]
             self._del_dest_WCS(fobj, target_ext)
             sipwcs = HSTWCS(self, ('SIPWCS', i))
             idckw = sipwcs._idc2hdr()
@@ -2035,19 +2042,19 @@ class Headerlet(fits.HDUList):
 
             fobj[target_ext].header.extend(priwcs[0].header)
             if sipwcs.cpdis1:
-                whdu = priwcs[('WCSDVARR', (i-1)*numnpol+1)].copy()
+                whdu = priwcs[('WCSDVARR', (i - 1) * numnpol + 1)].copy()
                 whdu.update_ext_version(self[('SIPWCS', i)].header['DP1.EXTVER'])
                 fobj.append(whdu)
             if sipwcs.cpdis2:
-                whdu = priwcs[('WCSDVARR', i*numnpol)].copy()
+                whdu = priwcs[('WCSDVARR', i * numnpol)].copy()
                 whdu.update_ext_version(self[('SIPWCS', i)].header['DP2.EXTVER'])
                 fobj.append(whdu)
-            if sipwcs.det2im1: #or sipwcs.det2im2:
-                whdu = priwcs[('D2IMARR', (i-1)*numd2im+1)].copy()
+            if sipwcs.det2im1:  # or sipwcs.det2im2:
+                whdu = priwcs[('D2IMARR', (i - 1) * numd2im + 1)].copy()
                 whdu.update_ext_version(self[('SIPWCS', i)].header['D2IM1.EXTVER'])
                 fobj.append(whdu)
             if sipwcs.det2im2:
-                whdu = priwcs[('D2IMARR', i*numd2im)].copy()
+                whdu = priwcs[('D2IMARR', i * numd2im)].copy()
                 whdu.update_ext_version(self[('SIPWCS', i)].header['D2IM2.EXTVER'])
                 fobj.append(whdu)
 
@@ -2070,7 +2077,6 @@ class Headerlet(fits.HDUList):
         if close_dest:
             fobj.close()
 
-
     def apply_as_alternate(self, fobj, attach=True, wcskey=None, wcsname=None):
         """
         Copy this headerlet as an alternate WCS to fobj
@@ -2098,17 +2104,19 @@ class Headerlet(fits.HDUList):
             if close_dest:
                 fobj.close()
             raise ValueError("Destination name does not match headerlet"
-                "Observation %s cannot  be updated with headerlet %s" % (fname, self.hdrname))
+                             "Observation %s cannot  be updated with"
+                             "headerlet %s" % (fname, self.hdrname))
 
         # Verify whether this headerlet has the same distortion
-        #found in the image being updated
+        # found in the image being updated
         dname = self.get_destination_model(fobj)
         dist_models_equal = self.equal_distmodel(dname)
         if not dist_models_equal:
             raise ValueError("Distortion models do not match \n"
                              "Headerlet: %s \n"
                              "Destination file: %s\n"
-            "attach_to_file() can be used to append this headerlet" %(self.distname, dname))
+                             "attach_to_file() can be used to append this headerlet" %
+                             (self.distname, dname))
 
         # Insure that WCSCORR table has been created with all original
         # WCS's recorded prior to adding the headerlet WCS
@@ -2148,12 +2156,12 @@ class Headerlet(fits.HDUList):
                 hwcs_header = altwcs.pc2cd(hwcs_header, key=wkey)
             for ax in range(1, hwcs.naxis + 1):
                 hwcs_header['CTYPE{0}{1}'.format(ax, wkey)] = \
-                           self[('SIPWCS', 1)].header['CTYPE{0}'.format(ax)]
+                    self[('SIPWCS', 1)].header['CTYPE{0}'.format(ax)]
             fhdr.extend(hwcs_header)
             fhdr['WCSNAME' + wkey] = wname
             # also update with HDRNAME (a non-WCS-standard kw)
             for kw in self.fit_kws:
-                #fhdr.insert(wind, pyfits.Card(kw + wkey,
+                # fhdr.insert(wind, pyfits.Card(kw + wkey,
                 #                              self[0].header[kw]))
                 fhdr.append(fits.Card(kw + wkey, self[0].header[kw]))
         # Update the WCSCORR table with new rows from the headerlet's WCSs
@@ -2210,7 +2218,7 @@ class Headerlet(fits.HDUList):
             fobj.close()
 
     def info(self, columns=None, pad=2, maxwidth=None,
-                output=None, clobber=True, quiet=False):
+             output=None, clobber=True, quiet=False):
         """
         Prints a summary of this headerlet
         The summary includes:
@@ -2240,7 +2248,7 @@ class Headerlet(fits.HDUList):
         """
         summary_cols, summary_dict = self.summary(columns=columns)
         print_summary(summary_cols, summary_dict, pad=pad, maxwidth=maxwidth,
-                        idcol=None, output=output, clobber=clobber, quiet=quiet)
+                      idcol=None, output=output, clobber=clobber, quiet=quiet)
 
     def summary(self, columns=None):
         """
@@ -2301,7 +2309,7 @@ class Headerlet(fits.HDUList):
         HDRNAME.
         """
         unique = verify_hdrname_is_unique(dest, self.hdrname)
-        logger.debug("verify_hdrname() returned %s"%unique)
+        logger.debug("verify_hdrname() returned %s" % unique)
         return unique
 
     def get_destination_model(self, dest):
@@ -2318,7 +2326,7 @@ class Headerlet(fits.HDUList):
         else:
             destim = dest
         dname = destim[0].header['DISTNAME'] if 'distname' in destim[0].header \
-              else self.build_distname(dest)
+            else self.build_distname(dest)
         if destim_opened:
             destim.close()
         return dname
@@ -2357,7 +2365,8 @@ class Headerlet(fits.HDUList):
         else:
             logger.debug("verify_destim() returned False")
             logger.critical("Destination name does not match headerlet. "
-                    "Observation %s cannot  be updated with headerlet %s" % (fname, self.hdrname))
+                            "Observation %s cannot  be updated with"
+                            "headerlet %s" % (fname, self.hdrname))
             return False
 
     def build_distname(self, dest):
@@ -2377,7 +2386,7 @@ class Headerlet(fits.HDUList):
         sipname, idctab = utils.build_sipname(dest, dest, None)
         npolname, npolfile = utils.build_npolname(dest, npolfile)
         d2imname, d2imfile = utils.build_d2imname(dest, d2imfile)
-        dname = utils.build_distname(sipname,npolname,d2imname)
+        dname = utils.build_distname(sipname, npolname, d2imname)
         return dname
 
     def tofile(self, fname, destim=None, hdrname=None, clobber=False):
@@ -2418,8 +2427,7 @@ class Headerlet(fits.HDUList):
         else:
             for idx in range(numext):
                 # Only delete WCS from extensions which may have WCS keywords
-                if ('XTENSION' in dest[idx].header and
-                    dest[idx].header['XTENSION'] == 'IMAGE'):
+                if ('XTENSION' in dest[idx].header and dest[idx].header['XTENSION'] == 'IMAGE'):
                     self._remove_d2im(dest[idx])
                     self._remove_sip(dest[idx])
                     self._remove_lut(dest[idx])
@@ -2427,12 +2435,7 @@ class Headerlet(fits.HDUList):
                     self._remove_idc_coeffs(dest[idx])
                     self._remove_fit_values(dest[idx])
         self._remove_ref_files(dest[0])
-        """
-        if not ext:
-            self._remove_alt_WCS(dest, ext=range(numext))
-        else:
-           self._remove_alt_WCS(dest, ext=ext)
-        """
+
     def _del_dest_WCS_ext(self, dest):
         numwdvarr = countExtn(dest, 'WCSDVARR')
         numd2im = countExtn(dest, 'D2IMARR')
@@ -2459,13 +2462,13 @@ class Headerlet(fits.HDUList):
         Remove the any existing astrometric fit values from a FITS extension
         """
 
-        logger.debug("Removing astrometric fit values from (%s, %s)"%
+        logger.debug("Removing astrometric fit values from (%s, %s)" %
                      (ext.name, ext.ver))
         dkeys = altwcs.wcskeys(ext.header)
-        if 'O' in dkeys: dkeys.remove('O') # Do not remove wcskey='O' values
+        if 'O' in dkeys: dkeys.remove('O')  # Do not remove wcskey='O' values
         for fitkw in ['NMATCH', 'CATALOG']:
             for k in dkeys:
-                fkw = (fitkw+k).rstrip()
+                fkw = (fitkw + k).rstrip()
                 if fkw in ext.header:
                     del ext.header[fkw]
 
@@ -2544,7 +2547,7 @@ class Headerlet(fits.HDUList):
         dkeys = altwcs.wcskeys(dest[('SCI', 1)].header)
         for val in ['O', '', ' ']:
             if val in dkeys:
-                dkeys.remove(val) # Never delete WCS with wcskey='O'
+                dkeys.remove(val)  # Never delete WCS with wcskey='O'
 
         logger.debug("Removing alternate WCSs with keys %s from %s"
                      % (dkeys, dest.filename()))
@@ -2588,6 +2591,7 @@ class Headerlet(fits.HDUList):
             except KeyError:
                 pass
 
+
 @with_logging
 def _idc2hdr(fromhdr, tohdr, towkey=' '):
     """
@@ -2598,7 +2602,7 @@ def _idc2hdr(fromhdr, tohdr, towkey=' '):
     coeffs = ['OCX10', 'OCX11', 'OCY10', 'OCY11', 'IDCSCALE']
     for c in coeffs:
         try:
-            tohdr[c+towkey] = fromhdr[c]
+            tohdr[c + towkey] = fromhdr[c]
             logger.debug("Copied %s to header")
         except KeyError:
             continue
@@ -2663,8 +2667,8 @@ def get_extname_extver_list(fobj, sciext):
         else:
             extlist = sciext[:]
     else:
-        errstr = "Expected sciext to be a list of FITS extensions with science data\n"+\
-              "    a valid EXTNAME string, or an integer."
+        errstr = "Expected sciext to be a list of FITS extensions with science data\n" + \
+            "    a valid EXTNAME string, or an integer."
         logger.critical(errstr)
         raise ValueError
     return extlist
diff --git a/stwcs/wcsutil/hstwcs.py b/stwcs/wcsutil/hstwcs.py
index bfebcfc..27f6467 100644
--- a/stwcs/wcsutil/hstwcs.py
+++ b/stwcs/wcsutil/hstwcs.py
@@ -1,25 +1,21 @@
-from __future__ import absolute_import, division, print_function # confidence high
+from __future__ import absolute_import, division, print_function
 
 import os
 from astropy.wcs import WCS
 from astropy.io import fits
-from stwcs.distortion import models, coeff_converter
+from ..distortion import models, coeff_converter
 import numpy as np
 from stsci.tools import fileutil
 
-from . import altwcs
+from . import pc2cd
 from . import getinput
-from . import mappings
 from . import instruments
 from .mappings import inst_mappings, ins_spec_kw
-from .mappings import basic_wcs
 
-__docformat__ = 'restructuredtext'
+__all__ = ['HSTWCS']
 
-#
-#### Utility functions copied from 'updatewcs.utils' to avoid circular imports
-#
-def extract_rootname(kwvalue,suffix=""):
+
+def extract_rootname(kwvalue, suffix=""):
     """ Returns the rootname from a full reference filename
 
         If a non-valid value (any of ['','N/A','NONE','INDEF',None]) is input,
@@ -28,13 +24,13 @@ def extract_rootname(kwvalue,suffix=""):
         This function will also replace any 'suffix' specified with a blank.
     """
     # check to see whether a valid kwvalue has been provided as input
-    if kwvalue.strip() in ['','N/A','NONE','INDEF',None]:
-        return 'NONE' # no valid value, so return 'NONE'
+    if kwvalue.strip() in ['', 'N/A', 'NONE', 'INDEF', None]:
+        return 'NONE'  # no valid value, so return 'NONE'
 
     # for a valid kwvalue, parse out the rootname
     # strip off any environment variable from input filename, if any are given
     if '$' in kwvalue:
-        fullval = kwvalue[kwvalue.find('$')+1:]
+        fullval = kwvalue[kwvalue.find('$') + 1:]
     else:
         fullval = kwvalue
     # Extract filename without path from kwvalue
@@ -44,12 +40,13 @@ def extract_rootname(kwvalue,suffix=""):
     rootname = fileutil.buildNewRootname(fname)
 
     # Now, remove any known suffix from rootname
-    rootname = rootname.replace(suffix,'')
+    rootname = rootname.replace(suffix, '')
     return rootname.strip()
 
+
 def build_default_wcsname(idctab):
 
-    idcname = extract_rootname(idctab,suffix='_idc')
+    idcname = extract_rootname(idctab, suffix='_idc')
     wcsname = 'IDC_' + idcname
     return wcsname
 
@@ -93,12 +90,9 @@ class NoConvergence(Exception):
         self.accuracy       = kwargs.pop('accuracy', None)
         self.niter          = kwargs.pop('niter', None)
         self.divergent      = kwargs.pop('divergent', None)
-        self.failed2converge= kwargs.pop('failed2converge', None)
+        self.failed2converge = kwargs.pop('failed2converge', None)
 
 
-#
-#### HSTWCS Class definition
-#
 class HSTWCS(WCS):
 
     def __init__(self, fobj=None, ext=None, minerr=0.0, wcskey=" "):
@@ -138,7 +132,6 @@ class HSTWCS(WCS):
             self.filename = filename
             instrument_name = hdr0.get('INSTRUME', 'DEFAULT')
             if instrument_name == 'DEFAULT' or instrument_name not in list(inst_mappings.keys()):
-                #['IRAF/ARTDATA','',' ','N/A']:
                 self.instrument = 'DEFAULT'
             else:
                 self.instrument = instrument_name
@@ -189,7 +182,7 @@ class HSTWCS(WCS):
         Reads in first order IDCTAB coefficients if present in the header
         """
         coeffs = ['ocx10', 'ocx11', 'ocy10', 'ocy11', 'idcscale',
-                    'idcv2ref','idcv3ref', 'idctheta']
+                  'idcv2ref', 'idcv3ref', 'idctheta']
         for c in coeffs:
             self.__setattr__(c, header.get(c, None))
 
@@ -225,7 +218,7 @@ class HSTWCS(WCS):
                         pass
 
         else:
-            raise KeyError("Unsupported instrument - %s" %self.instrument)
+            raise KeyError("Unsupported instrument - %s" % self.instrument)
 
     def setPscale(self):
         """
@@ -234,7 +227,7 @@ class HSTWCS(WCS):
         try:
             cd11 = self.wcs.cd[0][0]
             cd21 = self.wcs.cd[1][0]
-            self.pscale = np.sqrt(np.power(cd11,2)+np.power(cd21,2)) * 3600.
+            self.pscale = np.sqrt(np.power(cd11, 2) + np.power(cd21, 2)) * 3600.
         except AttributeError:
             if self.wcs.has_cd():
                 print("This file has a PC matrix. You may want to convert it \n \
@@ -249,7 +242,7 @@ class HSTWCS(WCS):
         try:
             cd12 = self.wcs.cd[0][1]
             cd22 = self.wcs.cd[1][1]
-            self.orientat = np.rad2deg(np.arctan2(cd12,cd22))
+            self.orientat = np.rad2deg(np.arctan2(cd12, cd22))
         except AttributeError:
             if self.wcs.has_cd():
                 print("This file has a PC matrix. You may want to convert it \n \
@@ -261,7 +254,7 @@ class HSTWCS(WCS):
         """
         Updates the CD matrix with a new plate scale
         """
-        self.wcs.cd = self.wcs.cd/self.pscale*scale
+        self.wcs.cd = self.wcs.cd / self.pscale * scale
         self.setPscale()
 
     def readModel(self, update=False, header=None):
@@ -282,8 +275,8 @@ class HSTWCS(WCS):
             CX10, CX11, CY10, CY11, IDCSCALE, IDCTHETA, IDCXREF, IDCYREF,
             IDCV2REF, IDCV3REF
         """
-        if self.idctab in [None, '', ' ','N/A']:
-            #Keyword idctab is not present in header - check for sip coefficients
+        if self.idctab in [None, '', ' ', 'N/A']:
+            # Keyword idctab is not present in header - check for sip coefficients
             if header is not None and 'IDCSCALE' in header:
                 self._readModelFromHeader(header)
             else:
@@ -319,7 +312,6 @@ class HSTWCS(WCS):
 
         self.idcmodel = model
 
-
     def readModelFromIDCTAB(self, header=None, update=False):
         """
         Read distortion model from idc table.
@@ -334,25 +326,26 @@ class HSTWCS(WCS):
             IDCV2REF, IDCV3REF
 
         """
-        if self.date_obs == None:
+        if self.date_obs is None:
             print('date_obs not available\n')
             self.idcmodel = None
             return
-        if self.filter1 == None and self.filter2 == None:
+        if self.filter1 is None and self.filter2 is None:
             'No filter information available\n'
             self.idcmodel = None
             return
 
         self.idcmodel = models.IDCModel(self.idctab,
-                    chip=self.chip, direction='forward', date=self.date_obs,
-                    filter1=self.filter1, filter2=self.filter2,
-                    offtab=self.offtab, binned=self.binned)
+                                        chip=self.chip, direction='forward',
+                                        date=self.date_obs,
+                                        filter1=self.filter1, filter2=self.filter2,
+                                        offtab=self.offtab, binned=self.binned)
 
         if self.ltv1 != 0. or self.ltv2 != 0.:
             self.resetLTV()
 
         if update:
-            if header==None:
+            if header is None:
                 print('Update header with IDC model kw requested but header was not provided\n.')
             else:
                 self._updatehdr(header)
@@ -393,7 +386,7 @@ class HSTWCS(WCS):
         if not wcskey:
             wcskey = self.wcs.alt
         if self.wcs.has_cd():
-            h = altwcs.pc2cd(h, key=wcskey)
+            h = pc2cd(h, key=wcskey)
 
         if 'wcsname' not in h:
             if self.idctab is not None:
@@ -440,13 +433,13 @@ class HSTWCS(WCS):
         k - one of 'a', 'b', 'ap', 'bp'
         """
 
-        cards = [] #fits.CardList()
-        korder = self.sip.__getattribute__(k+'_order')
-        cards.append(fits.Card(keyword=k.upper()+'_ORDER', value=korder))
+        cards = []
+        korder = self.sip.__getattribute__(k + '_order')
+        cards.append(fits.Card(keyword=k.upper() + '_ORDER', value=korder))
         coeffs = self.sip.__getattribute__(k)
         ind = coeffs.nonzero()
         for i in range(len(ind[0])):
-            card = fits.Card(keyword=k.upper()+'_'+str(ind[0][i])+'_'+str(ind[1][i]),
+            card = fits.Card(keyword=k.upper() + '_' + str(ind[0][i]) + '_' + str(ind[1][i]),
                              value=coeffs[ind[0][i], ind[1][i]])
             cards.append(card)
         return cards
@@ -454,7 +447,7 @@ class HSTWCS(WCS):
     def _idc2hdr(self):
         # save some of the idc coefficients
         coeffs = ['ocx10', 'ocx11', 'ocy10', 'ocy11', 'idcscale']
-        cards = [] #fits.CardList()
+        cards = []
         for c in coeffs:
             try:
                 val = self.__getattribute__(c)
@@ -711,27 +704,25 @@ adaptive=False, detect_divergence=False, quiet=False)
             try:
                 ra     = np.asarray(args[0], dtype=np.float64)
                 dec    = np.asarray(args[1], dtype=np.float64)
-                #assert( len(ra.shape) == 1 and len(dec.shape) == 1 )
+                # assert( len(ra.shape) == 1 and len(dec.shape) == 1 )
                 origin = int(args[2])
                 vect1D = True
             except:
-                raise TypeError("When providing three arguments, they must " \
-                            "be (Ra, Dec, origin) where Ra and Dec are " \
-                            "Nx1 vectors.")
+                raise TypeError("When providing three arguments, they must "
+                                "be (Ra, Dec, origin) where Ra and Dec are "
+                                "Nx1 vectors.")
         elif nargs == 2:
             try:
                 rd  = np.asarray(args[0], dtype=np.float64)
-                #assert( rd.shape[1] == 2 )
-                ra  = rd[:,0]
-                dec = rd[:,1]
+                ra  = rd[:, 0]
+                dec = rd[:, 1]
                 origin = int(args[1])
                 vect1D = False
             except:
-                raise TypeError("When providing two arguments, they must " \
-                            "be (RaDec, origin) where RaDec is a Nx2 array.")
+                raise TypeError("When providing two arguments, they must "
+                                "be (RaDec, origin) where RaDec is a Nx2 array.")
         else:
-            raise TypeError("Expected 2 or 3 arguments, {:d} given." \
-                            .format(nargs))
+            raise TypeError("Expected 2 or 3 arguments, {:d} given.".format(nargs))
 
         # process optional arguments:
         accuracy          = kwargs.pop('accuracy', 1.0e-4)
@@ -743,8 +734,8 @@ adaptive=False, detect_divergence=False, quiet=False)
         #####################################################################
         ##                INITIALIZE ITERATIVE PROCESS:                    ##
         #####################################################################
-        x0, y0 = self.wcs_world2pix(ra, dec, origin) # <-- initial approximation
-                                                  #     (WCS based only)
+        x0, y0 = self.wcs_world2pix(ra, dec, origin)  # <-- initial approximation
+                                                      #     (WCS based only)
 
         # see if an iterative solution is required (when any of the
         # non-CD-matrix corrections are present). If not required
@@ -757,17 +748,17 @@ adaptive=False, detect_divergence=False, quiet=False)
             if vect1D:
                 return [x0, y0]
             else:
-                return np.dstack([x0,y0])[0]
+                return np.dstack([x0, y0])[0]
 
-        x  = x0.copy() # 0-order solution
-        y  = y0.copy() # 0-order solution
+        x  = x0.copy()  # 0-order solution
+        y  = y0.copy()  # 0-order solution
 
         # initial correction:
         dx, dy = self.pix2foc(x, y, origin)
         # If pix2foc does not apply all the required distortion
         # corrections then replace the above line with:
-        #r0, d0 = self.all_pix2world(x, y, origin)
-        #dx, dy = self.wcs_world2pix(r0, d0, origin )
+        # r0, d0 = self.all_pix2world(x, y, origin)
+        # dx, dy = self.wcs_world2pix(r0, d0, origin )
         dx -= x0
         dy -= y0
 
@@ -776,21 +767,21 @@ adaptive=False, detect_divergence=False, quiet=False)
         y -= dy
 
         # norn (L2) squared of the correction:
-        dn2prev   = dx**2+dy**2
-        dn2       = dn2prev
+        dn2prev = dx ** 2 + dy ** 2
+        dn2 = dn2prev
 
         # prepare for iterative process
-        iterlist  = list(range(1, maxiter+1))
-        accuracy2 = accuracy**2
-        ind       = None
-        inddiv    = None
+        iterlist  = list(range(1, maxiter + 1))
+        accuracy2 = accuracy ** 2
+        ind = None
+        inddiv = None
 
-        npts      = x.shape[0]
+        npts = x.shape[0]
 
         # turn off numpy runtime warnings for 'invalid' and 'over':
         old_invalid = np.geterr()['invalid']
-        old_over    = np.geterr()['over']
-        np.seterr(invalid = 'ignore', over = 'ignore')
+        old_over = np.geterr()['over']
+        np.seterr(invalid='ignore', over='ignore')
 
         #####################################################################
         ##                     NON-ADAPTIVE ITERATIONS:                    ##
@@ -805,13 +796,13 @@ adaptive=False, detect_divergence=False, quiet=False)
                 dx, dy = self.pix2foc(x, y, origin)
                 # If pix2foc does not apply all the required distortion
                 # corrections then replace the above line with:
-                #r0, d0 = self.all_pix2world(x, y, origin)
-                #dx, dy = self.wcs_world2pix(r0, d0, origin )
+                # r0, d0 = self.all_pix2world(x, y, origin)
+                # dx, dy = self.wcs_world2pix(r0, d0, origin )
                 dx -= x0
                 dy -= y0
 
                 # update norn (L2) squared of the correction:
-                dn2 = dx**2+dy**2
+                dn2 = dx ** 2 + dy ** 2
 
                 # check for divergence (we do this in two stages
                 # to optimize performance for the most common
@@ -826,12 +817,12 @@ adaptive=False, detect_divergence=False, quiet=False)
                             x[ind] -= dx[ind]
                             y[ind] -= dy[ind]
                             # switch to adaptive iterations:
-                            ind, = np.where((dn2 >= accuracy2) & \
-                                        (dn2 <= dn2prev) & np.isfinite(dn2))
+                            ind, = np.where((dn2 >= accuracy2) &
+                                            (dn2 <= dn2prev) & np.isfinite(dn2))
                             iterlist = iterlist[k:]
                             adaptive = True
                             break
-                    #dn2prev[ind] = dn2[ind]
+                    # dn2prev[ind] = dn2[ind]
                     dn2prev = dn2
 
                 # apply correction:
@@ -854,22 +845,22 @@ adaptive=False, detect_divergence=False, quiet=False)
                 dx[ind], dy[ind] = self.pix2foc(x[ind], y[ind], origin)
                 # If pix2foc does not apply all the required distortion
                 # corrections then replace the above line with:
-                #r0[ind], d0[ind] = self.all_pix2world(x[ind], y[ind], origin)
-                #dx[ind], dy[ind] = self.wcs_world2pix(r0[ind], d0[ind], origin)
+                # r0[ind], d0[ind] = self.all_pix2world(x[ind], y[ind], origin)
+                # dx[ind], dy[ind] = self.wcs_world2pix(r0[ind], d0[ind], origin)
                 dx[ind] -= x0[ind]
                 dy[ind] -= y0[ind]
 
                 # update norn (L2) squared of the correction:
-                dn2 = dx**2+dy**2
+                dn2 = dx ** 2 + dy ** 2
 
                 # update indices of elements that still need correction:
                 if detect_divergence:
                     ind, = np.where((dn2 >= accuracy2) & (dn2 <= dn2prev))
-                    #ind = ind[np.where((dn2[ind] >= accuracy2) & (dn2[ind] <= dn2prev))]
+                    # ind = ind[np.where((dn2[ind] >= accuracy2) & (dn2[ind] <= dn2prev))]
                     dn2prev[ind] = dn2[ind]
                 else:
                     ind, = np.where(dn2 >= accuracy2)
-                    #ind = ind[np.where(dn2[ind] >= accuracy2)]
+                    # ind = ind[np.where(dn2[ind] >= accuracy2)]
 
                 # apply correction:
                 x[ind] -= dx[ind]
@@ -880,9 +871,9 @@ adaptive=False, detect_divergence=False, quiet=False)
         ##         AND FAILED-TO-CONVERGE POINTS                           ##
         #####################################################################
         # Identify diverging and/or invalid points:
-        invalid = (((~np.isfinite(y)) | (~np.isfinite(x)) | \
-                    (~np.isfinite(dn2))) & \
-                   (np.isfinite(ra)) &  (np.isfinite(dec)))
+        invalid = (((~np.isfinite(y)) | (~np.isfinite(x)) |
+                    (~np.isfinite(dn2))) &
+                   (np.isfinite(ra)) & (np.isfinite(dec)))
         # When detect_divergence==False, dn2prev is outdated (it is the
         # norm^2 of the very first correction). Still better than nothing...
         inddiv, = np.where(((dn2 >= accuracy2) & (dn2 > dn2prev)) | invalid)
@@ -891,7 +882,7 @@ adaptive=False, detect_divergence=False, quiet=False)
         # identify points that did not converge within
         # 'maxiter' iterations:
         if k >= maxiter:
-            ind,= np.where((dn2 >= accuracy2) & (dn2 <= dn2prev) & (~invalid))
+            ind, = np.where((dn2 >= accuracy2) & (dn2 <= dn2prev) & (~invalid))
             if ind.shape[0] == 0:
                 ind = None
         else:
@@ -907,50 +898,50 @@ adaptive=False, detect_divergence=False, quiet=False)
                 sol  = [x, y]
                 err  = [np.abs(dx), np.abs(dy)]
             else:
-                sol  = np.dstack( [x, y] )[0]
-                err  = np.dstack( [np.abs(dx), np.abs(dy)] )[0]
+                sol  = np.dstack([x, y] )[0]
+                err  = np.dstack([np.abs(dx), np.abs(dy)] )[0]
 
             # restore previous numpy error settings:
-            np.seterr(invalid = old_invalid, over = old_over)
+            np.seterr(invalid=old_invalid, over=old_over)
 
             if inddiv is None:
-                raise NoConvergence("'HSTWCS.all_world2pix' failed to "        \
-                    "converge to the requested accuracy after {:d} "         \
-                    "iterations.".format(k), best_solution = sol,            \
-                    accuracy = err, niter = k, failed2converge = ind,        \
-                    divergent = None)
+                raise NoConvergence("'HSTWCS.all_world2pix' failed to "
+                                    "converge to the requested accuracy after {:d} "
+                                    "iterations.".format(k), best_solution=sol,
+                                    accuracy=err, niter=k, failed2converge=ind,
+                                    divergent=None)
             else:
-                raise NoConvergence("'HSTWCS.all_world2pix' failed to "        \
-                    "converge to the requested accuracy.{0:s}"               \
-                    "After {1:d} iterations, the solution is diverging "     \
-                    "at least for one input point."                          \
-                    .format(os.linesep, k), best_solution = sol,             \
-                    accuracy = err, niter = k, failed2converge = ind,        \
-                    divergent = inddiv)
+                raise NoConvergence("'HSTWCS.all_world2pix' failed to "
+                                    "converge to the requested accuracy.{0:s}"
+                                    "After {1:d} iterations, the solution is diverging "
+                                    "at least for one input point."
+                                    .format(os.linesep, k), best_solution=sol,
+                                    accuracy=err, niter=k, failed2converge=ind,
+                                    divergent=inddiv)
 
         #####################################################################
         ##             FINALIZE AND FORMAT DATA FOR RETURN:                ##
         #####################################################################
         # restore previous numpy error settings:
-        np.seterr(invalid = old_invalid, over = old_over)
+        np.seterr(invalid=old_invalid, over=old_over)
 
         if vect1D:
             return [x, y]
         else:
-            return np.dstack( [x, y] )[0]
+            return np.dstack([x, y] )[0]
 
     def _updatehdr(self, ext_hdr):
-        #kw2add : OCX10, OCX11, OCY10, OCY11
+        # kw2add : OCX10, OCX11, OCY10, OCY11
         # record the model in the header for use by pydrizzle
-        ext_hdr['OCX10'] = self.idcmodel.cx[1,0]
-        ext_hdr['OCX11'] = self.idcmodel.cx[1,1]
-        ext_hdr['OCY10'] = self.idcmodel.cy[1,0]
-        ext_hdr['OCY11'] = self.idcmodel.cy[1,1]
+        ext_hdr['OCX10'] = self.idcmodel.cx[1, 0]
+        ext_hdr['OCX11'] = self.idcmodel.cx[1, 1]
+        ext_hdr['OCY10'] = self.idcmodel.cy[1, 0]
+        ext_hdr['OCY11'] = self.idcmodel.cy[1, 1]
         ext_hdr['IDCSCALE'] = self.idcmodel.refpix['PSCALE']
         ext_hdr['IDCTHETA'] = self.idcmodel.refpix['THETA']
         ext_hdr['IDCXREF'] = self.idcmodel.refpix['XREF']
         ext_hdr['IDCYREF'] = self.idcmodel.refpix['YREF']
-        ext_hdr['IDCV2REF'] =  self.idcmodel.refpix['V2REF']
+        ext_hdr['IDCV2REF'] = self.idcmodel.refpix['V2REF']
         ext_hdr['IDCV3REF'] = self.idcmodel.refpix['V3REF']
 
     def printwcs(self):
@@ -958,8 +949,8 @@ adaptive=False, detect_divergence=False, quiet=False)
         Print the basic WCS keywords.
         """
         print('WCS Keywords\n')
-        print('CD_11  CD_12: %r %r' % (self.wcs.cd[0,0],  self.wcs.cd[0,1]))
-        print('CD_21  CD_22: %r %r' % (self.wcs.cd[1,0],  self.wcs.cd[1,1]))
+        print('CD_11  CD_12: %r %r' % (self.wcs.cd[0, 0], self.wcs.cd[0, 1]))
+        print('CD_21  CD_22: %r %r' % (self.wcs.cd[1, 0], self.wcs.cd[1, 1]))
         print('CRVAL    : %r %r' % (self.wcs.crval[0], self.wcs.crval[1]))
         print('CRPIX    : %r %r' % (self.wcs.crpix[0], self.wcs.crpix[1]))
         print('NAXIS    : %d %d' % (self.naxis1, self.naxis2))
diff --git a/stwcs/wcsutil/instruments.py b/stwcs/wcsutil/instruments.py
index f662513..83fb1bd 100644
--- a/stwcs/wcsutil/instruments.py
+++ b/stwcs/wcsutil/instruments.py
@@ -1,6 +1,5 @@
-from __future__ import absolute_import, division, print_function # confidence high
+from __future__ import absolute_import, division, print_function
 
-from .mappings import ins_spec_kw
 
 class InstrWCS(object):
     """
@@ -135,13 +134,14 @@ class InstrWCS(object):
             self.chip = 1
 
     def set_parity(self):
-        self.parity = [[1.0,0.0],[0.0,-1.0]]
+        self.parity = [[1.0, 0.0], [0.0, -1.0]]
 
     def set_detector(self):
         # each instrument has a different kw for detector and it can be
         # in a different header, so this is to be handled by the instrument classes
         self.detector = 'DEFAULT'
 
+
 class ACSWCS(InstrWCS):
     """
     get instrument specific kw
@@ -150,7 +150,7 @@ class ACSWCS(InstrWCS):
     def __init__(self, hdr0, hdr):
         self.primhdr = hdr0
         self.exthdr = hdr
-        InstrWCS.__init__(self,hdr0, hdr)
+        InstrWCS.__init__(self, hdr0, hdr)
         self.set_ins_spec_kw()
 
     def set_detector(self):
@@ -161,9 +161,9 @@ class ACSWCS(InstrWCS):
             raise
 
     def set_parity(self):
-        parity = {'WFC':[[1.0,0.0],[0.0,-1.0]],
-                'HRC':[[-1.0,0.0],[0.0,1.0]],
-                'SBC':[[-1.0,0.0],[0.0,1.0]]}
+        parity = {'WFC': [[1.0, 0.0], [0.0, -1.0]],
+                  'HRC': [[-1.0, 0.0], [0.0, 1.0]],
+                  'SBC': [[-1.0, 0.0], [0.0, 1.0]]}
 
         if self.detector not in list(parity.keys()):
             parity = InstrWCS.set_parity(self)
@@ -173,24 +173,22 @@ class ACSWCS(InstrWCS):
 
 class WFPC2WCS(InstrWCS):
 
-
     def __init__(self, hdr0, hdr):
         self.primhdr = hdr0
         self.exthdr = hdr
-        InstrWCS.__init__(self,hdr0, hdr)
+        InstrWCS.__init__(self, hdr0, hdr)
         self.set_ins_spec_kw()
 
     def set_filter1(self):
         self.filter1 = self.primhdr.get('FILTNAM1', None)
-        if self.filter1 == " " or self.filter1 == None:
+        if self.filter1 == " " or self.filter1 is None:
             self.filter1 = 'CLEAR1'
 
     def set_filter2(self):
         self.filter2 = self.primhdr.get('FILTNAM2', None)
-        if self.filter2 == " " or self.filter2 == None:
+        if self.filter2 == " " or self.filter2 is None:
             self.filter2 = 'CLEAR2'
 
-
     def set_binned(self):
         mode = self.primhdr.get('MODE', 1)
         if mode == 'FULL':
@@ -202,7 +200,7 @@ class WFPC2WCS(InstrWCS):
         self.chip = self.exthdr.get('DETECTOR', 1)
 
     def set_parity(self):
-        self.parity = [[-1.0,0.],[0.,1.0]]
+        self.parity = [[-1.0, 0.], [0., 1.0]]
 
     def set_detector(self):
         try:
@@ -220,7 +218,7 @@ class WFC3WCS(InstrWCS):
     def __init__(self, hdr0, hdr):
         self.primhdr = hdr0
         self.exthdr = hdr
-        InstrWCS.__init__(self,hdr0, hdr)
+        InstrWCS.__init__(self, hdr0, hdr)
         self.set_ins_spec_kw()
 
     def set_detector(self):
@@ -232,22 +230,23 @@ class WFC3WCS(InstrWCS):
 
     def set_filter1(self):
         self.filter1 = self.primhdr.get('FILTER', None)
-        if self.filter1 == " " or self.filter1 == None:
+        if self.filter1 == " " or self.filter1 is None:
             self.filter1 = 'CLEAR'
 
     def set_filter2(self):
-        #Nicmos idc tables do not allow 2 filters.
+        # Nicmos idc tables do not allow 2 filters.
         self.filter2 = 'CLEAR'
 
     def set_parity(self):
-        parity = {'UVIS':[[-1.0,0.0],[0.0,1.0]],
-          'IR':[[-1.0,0.0],[0.0,1.0]]}
+        parity = {'UVIS': [[-1.0, 0.0], [0.0, 1.0]],
+                  'IR': [[-1.0, 0.0], [0.0, 1.0]]}
 
         if self.detector not in list(parity.keys()):
             parity = InstrWCS.set_parity(self)
         else:
             self.parity = parity[self.detector]
 
+
 class NICMOSWCS(InstrWCS):
     """
     Create a NICMOS specific class
@@ -256,19 +255,19 @@ class NICMOSWCS(InstrWCS):
     def __init__(self, hdr0, hdr):
         self.primhdr = hdr0
         self.exthdr = hdr
-        InstrWCS.__init__(self,hdr0, hdr)
+        InstrWCS.__init__(self, hdr0, hdr)
         self.set_ins_spec_kw()
 
     def set_parity(self):
-        self.parity = [[-1.0,0.],[0.,1.0]]
+        self.parity = [[-1.0, 0.], [0., 1.0]]
 
     def set_filter1(self):
         self.filter1 = self.primhdr.get('FILTER', None)
-        if self.filter1 == " " or self.filter1 == None:
+        if self.filter1 == " " or self.filter1 is None:
             self.filter1 = 'CLEAR'
 
     def set_filter2(self):
-        #Nicmos idc tables do not allow 2 filters.
+        # Nicmos idc tables do not allow 2 filters.
         self.filter2 = 'CLEAR'
 
     def set_chip(self):
@@ -281,6 +280,7 @@ class NICMOSWCS(InstrWCS):
             print('ERROR: Detector kw not found.\n')
             raise
 
+
 class STISWCS(InstrWCS):
     """
     A STIS specific class
@@ -289,20 +289,20 @@ class STISWCS(InstrWCS):
     def __init__(self, hdr0, hdr):
         self.primhdr = hdr0
         self.exthdr = hdr
-        InstrWCS.__init__(self,hdr0, hdr)
+        InstrWCS.__init__(self, hdr0, hdr)
         self.set_ins_spec_kw()
 
     def set_parity(self):
-        self.parity = [[-1.0,0.],[0.,1.0]]
+        self.parity = [[-1.0, 0.], [0., 1.0]]
 
     def set_filter1(self):
         self.filter1 = self.exthdr.get('OPT_ELEM', None)
-        if self.filter1 == " " or self.filter1 == None:
+        if self.filter1 == " " or self.filter1 is None:
             self.filter1 = 'CLEAR1'
 
     def set_filter2(self):
         self.filter2 = self.exthdr.get('FILTER', None)
-        if self.filter2 == " " or self.filter2 == None:
+        if self.filter2 == " " or self.filter2 is None:
             self.filter2 = 'CLEAR2'
 
     def set_detector(self):
diff --git a/stwcs/wcsutil/mappings.py b/stwcs/wcsutil/mappings.py
index 24038bf..a85df13 100644
--- a/stwcs/wcsutil/mappings.py
+++ b/stwcs/wcsutil/mappings.py
@@ -1,29 +1,29 @@
-from __future__ import division # confidence high
+from __future__ import division
 
 # This dictionary maps an instrument into an instrument class
 # The instrument class handles instrument specific keywords
 
-inst_mappings={'WFPC2': 'WFPC2WCS',
-                'ACS': 'ACSWCS',
-                'NICMOS': 'NICMOSWCS',
-                'STIS': 'STISWCS',
-                'WFC3': 'WFC3WCS',
-                'DEFAULT': 'InstrWCS'
-                }
+inst_mappings = {'WFPC2': 'WFPC2WCS',
+                 'ACS': 'ACSWCS',
+                 'NICMOS': 'NICMOSWCS',
+                 'STIS': 'STISWCS',
+                 'WFC3': 'WFC3WCS',
+                 'DEFAULT': 'InstrWCS'
+                 }
 
 
 # A list of instrument specific keywords
 # Every instrument class must have methods which define each of these
 # as class attributes.
-ins_spec_kw = [ 'idctab', 'offtab', 'date_obs', 'ra_targ', 'dec_targ', 'pav3', \
-                'detector', 'ltv1', 'ltv2', 'parity', 'binned','vafactor', \
-                'chip', 'naxis1', 'naxis2', 'filter1', 'filter2']
+ins_spec_kw = ['idctab', 'offtab', 'date_obs', 'ra_targ', 'dec_targ',
+               'pav3', 'detector', 'ltv1', 'ltv2', 'parity', 'binned',
+               'vafactor', 'chip', 'naxis1', 'naxis2', 'filter1', 'filter2']
 
 # A list of keywords defined in the primary header.
-# The HSTWCS class sets this as attributes 
-prim_hdr_kw = ['detector', 'offtab', 'idctab', 'date-obs', 
-              'pa_v3', 'ra_targ', 'dec_targ']
+# The HSTWCS class sets this as attributes
+prim_hdr_kw = ['detector', 'offtab', 'idctab', 'date-obs',
+               'pa_v3', 'ra_targ', 'dec_targ']
 
 # These are the keywords which are archived before MakeWCS is run
-basic_wcs = ['CD1_', 'CD2_', 'CRVAL', 'CTYPE', 'CRPIX', 'CTYPE', 'CDELT', 'CUNIT']
-            
+basic_wcs = ['CD1_', 'CD2_', 'CRVAL', 'CTYPE', 'CRPIX', 'CTYPE',
+             'CDELT', 'CUNIT']
diff --git a/stwcs/wcsutil/mosaic.py b/stwcs/wcsutil/mosaic.py
index 9d2d0a3..a757e0c 100644
--- a/stwcs/wcsutil/mosaic.py
+++ b/stwcs/wcsutil/mosaic.py
@@ -1,15 +1,17 @@
-from __future__ import division, print_function
+from __future__ import absolute_import, division, print_function
 import numpy as np
 from matplotlib import pyplot as plt
 from astropy.io import fits
 import string
 
 from stsci.tools import parseinput, irafglob
-from stwcs.distortion import utils
-from stwcs import updatewcs, wcsutil
-from stwcs.wcsutil import altwcs
+from ..distortion import utils
+from .. import wcsutil
+from ..wcsutil import altwcs
 
-def vmosaic(fnames, outwcs=None, ref_wcs=None, ext=None, extname=None, undistort=True, wkey='V', wname='VirtualMosaic', plot=False, clobber=False):
+
+def vmosaic(fnames, outwcs=None, ref_wcs=None, ext=None, extname=None, undistort=True,
+            wkey='V', wname='VirtualMosaic', plot=False, clobber=False):
     """
     Create a virtual mosaic using the WCS of the input images.
 
@@ -61,27 +63,29 @@ def vmosaic(fnames, outwcs=None, ref_wcs=None, ext=None, extname=None, undistort
        tangent plane and the virtual WCS is recorded in the header.
     """
     wcsobjects = readWCS(fnames, ext, extname)
-    if outwcs != None:
+    if outwcs is not None:
         outwcs = outwcs.deepcopy()
     else:
-        if ref_wcs != None:
+        if ref_wcs is not None:
             outwcs = utils.output_wcs(wcsobjects, ref_wcs=ref_wcs, undistort=undistort)
         else:
             outwcs = utils.output_wcs(wcsobjects, undistort=undistort)
     if plot:
-        outc=np.array([[0.,0], [outwcs._naxis1, 0],
-                             [outwcs._naxis1, outwcs._naxis2],
-                             [0, outwcs._naxis2], [0, 0]])
-        plt.plot(outc[:,0], outc[:,1])
+        outc = np.array([[0., 0], [outwcs._naxis1, 0],
+                         [outwcs._naxis1, outwcs._naxis2],
+                         [0, outwcs._naxis2], [0, 0]])
+        plt.plot(outc[:, 0], outc[:, 1])
     for wobj in wcsobjects:
-        outcorners = outwcs.wcs_world2pix(wobj.calc_footprint(),1)
+        outcorners = outwcs.wcs_world2pix(wobj.calc_footprint(), 1)
         if plot:
-            plt.plot(outcorners[:,0], outcorners[:,1])
+            plt.plot(outcorners[:, 0], outcorners[:, 1])
         objwcs = outwcs.deepcopy()
         objwcs.wcs.crpix = objwcs.wcs.crpix - (outcorners[0])
-        updatehdr(wobj.filename, objwcs,wkey=wkey, wcsname=wname, ext=wobj.extname, clobber=clobber)
+        updatehdr(wobj.filename, objwcs, wkey=wkey, wcsname=wname, ext=wobj.extname,
+                  clobber=clobber)
     return outwcs
 
+
 def updatehdr(fname, wcsobj, wkey, wcsname, ext=1, clobber=False):
     hdr = fits.getheader(fname, ext=ext)
     all_keys = list(string.ascii_uppercase)
@@ -89,7 +93,9 @@ def updatehdr(fname, wcsobj, wkey, wcsname, ext=1, clobber=False):
         raise KeyError("wkey must be one character: A-Z")
     if wkey not in altwcs.available_wcskeys(hdr):
         if not clobber:
-            raise ValueError("wkey %s is already in use. Use clobber=True to overwrite it or specify a different key." %wkey)
+            raise ValueError("wkey {0} is already in use."
+                             "Use clobber=True to overwrite it or"
+                             "specify a different key.".format(wkey))
         else:
             altwcs.deleteWCS(fname, ext=ext, wcskey='V')
     f = fits.open(fname, mode='update')
@@ -98,24 +104,25 @@ def updatehdr(fname, wcsobj, wkey, wcsname, ext=1, clobber=False):
     wcsnamekey = 'WCSNAME' + wkey
     f[ext].header[wcsnamekey] = wcsname
     for k in hwcs:
-        f[ext].header[k[:7]+wkey] = hwcs[k]
+        f[ext].header[k[: 7] + wkey] = hwcs[k]
 
     f.close()
 
-def wcs2header(wcsobj):
 
+def wcs2header(wcsobj):
     h = wcsobj.to_header()
 
     if wcsobj.wcs.has_cd():
         altwcs.pc2cd(h)
     h['CTYPE1'] = 'RA---TAN'
     h['CTYPE2'] = 'DEC--TAN'
-    norient = np.rad2deg(np.arctan2(h['CD1_2'],h['CD2_2']))
-    #okey = 'ORIENT%s' % wkey
+    norient = np.rad2deg(np.arctan2(h['CD1_2'], h['CD2_2']))
+    # okey = 'ORIENT%s' % wkey
     okey = 'ORIENT'
     h[okey] = norient
     return h
 
+
 def readWCS(input, exts=None, extname=None):
     if isinstance(input, str):
         if input[0] == '@':
@@ -134,15 +141,15 @@ def readWCS(input, exts=None, extname=None):
     wcso = []
     fomited = []
     # figure out which FITS extension(s) to use
-    if exts == None and extname == None:
-        #Assume it's simple FITS and the data is in the primary HDU
+    if exts is None and extname is None:
+        # Assume it's simple FITS and the data is in the primary HDU
         for f in filelist:
             try:
                 wcso = wcsutil.HSTWCS(f)
             except AttributeError:
                 fomited.append(f)
                 continue
-    elif exts != None and validateExt(exts):
+    elif exts is not None and validateExt(exts):
         exts = [exts]
         for f in filelist:
             try:
@@ -150,7 +157,7 @@ def readWCS(input, exts=None, extname=None):
             except KeyError:
                 fomited.append(f)
                 continue
-    elif extname != None:
+    elif extname is not None:
         for f in filelist:
             fobj = fits.open(f)
             for i in range(len(fobj)):
@@ -159,7 +166,7 @@ def readWCS(input, exts=None, extname=None):
                 except KeyError:
                     continue
                 if ename.lower() == extname.lower():
-                    wcso.append(wcsutil.HSTWCS(f,ext=i))
+                    wcso.append(wcsutil.HSTWCS(f, ext=i))
                 else:
                     continue
             fobj.close()
@@ -179,5 +186,3 @@ def validateExt(ext):
     else:
         return True
 
-
-
diff --git a/stwcs/wcsutil/wcscorr.py b/stwcs/wcsutil/wcscorr.py
index 3f9b7d5..48a1978 100644
--- a/stwcs/wcsutil/wcscorr.py
+++ b/stwcs/wcsutil/wcscorr.py
@@ -1,21 +1,20 @@
 from __future__ import absolute_import, division, print_function
 
-import os,copy
+import copy
 import numpy as np
 from astropy.io import fits
 
 import stwcs
-from stwcs.wcsutil import altwcs
-from stwcs.updatewcs import utils
+from . import altwcs
+from ..updatewcs import utils
 from stsci.tools import fileutil
-from . import convertwcs
 
-DEFAULT_WCS_KEYS = ['CRVAL1','CRVAL2','CRPIX1','CRPIX2',
-                    'CD1_1','CD1_2','CD2_1','CD2_2',
-                    'CTYPE1','CTYPE2','ORIENTAT']
-DEFAULT_PRI_KEYS = ['HDRNAME','SIPNAME','NPOLNAME','D2IMNAME','DESCRIP']
-COL_FITSKW_DICT = {'RMS_RA':'sci.crder1','RMS_DEC':'sci.crder2',
-                'NMatch':'sci.nmatch','Catalog':'sci.catalog'}
+DEFAULT_WCS_KEYS = ['CRVAL1', 'CRVAL2', 'CRPIX1', 'CRPIX2',
+                    'CD1_1', 'CD1_2', 'CD2_1', 'CD2_2',
+                    'CTYPE1', 'CTYPE2', 'ORIENTAT']
+DEFAULT_PRI_KEYS = ['HDRNAME', 'SIPNAME', 'NPOLNAME', 'D2IMNAME', 'DESCRIP']
+COL_FITSKW_DICT = {'RMS_RA': 'sci.crder1', 'RMS_DEC': 'sci.crder2',
+                   'NMatch': 'sci.nmatch', 'Catalog': 'sci.catalog'}
 
 ###
 ### WCSEXT table related keyword archive functions
@@ -53,7 +52,7 @@ def init_wcscorr(input, force=False):
             return
         else:
             del fimg['wcscorr']
-    print('Initializing new WCSCORR table for ',fimg.filename())
+    print('Initializing new WCSCORR table for ', fimg.filename())
 
     used_wcskeys = altwcs.wcskeys(fimg['SCI', 1].header)
 
@@ -64,14 +63,14 @@ def init_wcscorr(input, force=False):
 
     # create new table with more rows than needed initially to make it easier to
     # add new rows later
-    wcsext = create_wcscorr(descrip=True,numrows=numsci, padding=(numsci*numwcs) + numsci * 4)
+    wcsext = create_wcscorr(descrip=True, numrows=numsci, padding=(numsci * numwcs) + numsci * 4)
     # Assign the correct EXTNAME value to this table extension
     wcsext.header['TROWS'] = (numsci * 2, 'Number of updated rows in table')
     wcsext.header['EXTNAME'] = ('WCSCORR', 'Table with WCS Update history')
     wcsext.header['EXTVER'] = 1
 
     # define set of WCS keywords which need to be managed and copied to the table
-    wcs1 = stwcs.wcsutil.HSTWCS(fimg,ext=('SCI',1))
+    wcs1 = stwcs.wcsutil.HSTWCS(fimg, ext=('SCI', 1))
     idc2header = True
     if wcs1.idcscale is None:
         idc2header = False
@@ -79,18 +78,18 @@ def init_wcscorr(input, force=False):
 
     prihdr = fimg[0].header
     prihdr_keys = DEFAULT_PRI_KEYS
-    pri_funcs = {'SIPNAME':stwcs.updatewcs.utils.build_sipname,
-                 'NPOLNAME':stwcs.updatewcs.utils.build_npolname,
-                 'D2IMNAME':stwcs.updatewcs.utils.build_d2imname}
+    pri_funcs = {'SIPNAME': stwcs.updatewcs.utils.build_sipname,
+                 'NPOLNAME': stwcs.updatewcs.utils.build_npolname,
+                 'D2IMNAME': stwcs.updatewcs.utils.build_d2imname}
 
     # Now copy original OPUS values into table
     for extver in range(1, numsci + 1):
         rowind = find_wcscorr_row(wcsext.data,
                                   {'WCS_ID': 'OPUS', 'EXTVER': extver,
-                                   'WCS_key':'O'})
+                                   'WCS_key': 'O'})
         # There should only EVER be a single row for each extension with OPUS values
         rownum = np.where(rowind)[0][0]
-        #print 'Archiving OPUS WCS in row number ',rownum,' in WCSCORR table for SCI,',extver
+        # print 'Archiving OPUS WCS in row number ',rownum,' in WCSCORR table for SCI,',extver
 
         hdr = fimg['SCI', extver].header
         # define set of WCS keywords which need to be managed and copied to the table
@@ -100,7 +99,7 @@ def init_wcscorr(input, force=False):
         # if so, get its values directly, otherwise, archive the PRIMARY WCS
         # as the OPUS values in the WCSCORR table
         if 'O' not in used_wcskeys:
-            altwcs.archiveWCS(fimg,('SCI',extver),wcskey='O', wcsname='OPUS')
+            altwcs.archiveWCS(fimg, ('SCI', extver), wcskey='O', wcsname='OPUS')
         wkey = 'O'
 
         wcs = stwcs.wcsutil.HSTWCS(fimg, ext=('SCI', extver), wcskey=wkey)
@@ -113,7 +112,7 @@ def init_wcscorr(input, force=False):
             break
         for key in wcs_keywords:
             if key in wcsext.data.names:
-                wcsext.data.field(key)[rownum] = wcshdr[(key+wkey)[:8]]
+                wcsext.data.field(key)[rownum] = wcshdr[(key + wkey)[:8]]
         # Now get any keywords from PRIMARY header needed for WCS updates
         for key in prihdr_keys:
             if key in prihdr:
@@ -143,7 +142,7 @@ def init_wcscorr(input, force=False):
 
             # identify next empty row
             rowind = find_wcscorr_row(wcsext.data,
-                                    selections={'wcs_id':['','0.0']})
+                                      selections={'wcs_id': ['', '0.0']})
             rows = np.where(rowind)
             if len(rows[0]) > 0:
                 rownum = np.where(rowind)[0][0]
@@ -196,26 +195,26 @@ def find_wcscorr_row(wcstab, selections):
     mask = None
     for i in selections:
         icol = wcstab.field(i)
-        if isinstance(icol,np.chararray): icol = icol.rstrip()
+        if isinstance(icol, np.chararray): icol = icol.rstrip()
         selecti = selections[i]
-        if not isinstance(selecti,list):
-            if isinstance(selecti,str):
+        if not isinstance(selecti, list):
+            if isinstance(selecti, str):
                 selecti = selecti.rstrip()
             bmask = (icol == selecti)
             if mask is None:
                 mask = bmask.copy()
             else:
-                mask = np.logical_and(mask,bmask)
+                mask = np.logical_and(mask, bmask)
             del bmask
         else:
             for si in selecti:
-                if isinstance(si,str):
+                if isinstance(si, str):
                     si = si.rstrip()
                 bmask = (icol == si)
                 if mask is None:
                     mask = bmask.copy()
                 else:
-                    mask = np.logical_or(mask,bmask)
+                    mask = np.logical_or(mask, bmask)
                 del bmask
 
     return mask
@@ -268,7 +267,7 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
         headerlet
     """
     if not isinstance(dest, fits.HDUList):
-        dest = fits.open(dest,mode='update')
+        dest = fits.open(dest, mode='update')
     fname = dest.filename()
 
     if source is None:
@@ -280,7 +279,7 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
     numext = fileutil.countExtn(source, extname)
     if numext == 0:
         raise ValueError('No %s extensions found in the source HDU list.'
-                        % extname)
+                         % extname)
     # Initialize the WCSCORR table extension in dest if not already present
     init_wcscorr(dest)
     try:
@@ -291,7 +290,7 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
     # check to see whether or not this is an up-to-date table
     # replace with newly initialized table with current format
     old_table = dest['WCSCORR']
-    wcscorr_cols = ['WCS_ID','EXTVER', 'SIPNAME',
+    wcscorr_cols = ['WCS_ID', 'EXTVER', 'SIPNAME',
                     'HDRNAME', 'NPOLNAME', 'D2IMNAME']
 
     for colname in wcscorr_cols:
@@ -308,7 +307,7 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
     # modified...
     wcs_keys = altwcs.wcskeys(source[(extname, 1)].header)
     wcs_keys = [kk for kk in wcs_keys if kk]
-    if ' ' not in wcs_keys: wcs_keys.append(' ') # Insure that primary WCS gets used
+    if ' ' not in wcs_keys: wcs_keys.append(' ')  # Insure that primary WCS gets used
     # apply logic for only updating WCSCORR table with specified keywords
     # corresponding to the WCS with WCSNAME=wcs_id
     if wcs_id is not None:
@@ -324,10 +323,10 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
     wcs_keywords = list(wcshdr.keys())
 
     if 'O' in wcs_keys:
-        wcs_keys.remove('O') # 'O' is reserved for original OPUS WCS
+        wcs_keys.remove('O')  # 'O' is reserved for original OPUS WCS
 
     # create new table for hdr and populate it with the newly updated values
-    new_table = create_wcscorr(descrip=True,numrows=0, padding=len(wcs_keys)*numext)
+    new_table = create_wcscorr(descrip=True, numrows=0, padding=len(wcs_keys) * numext)
     prihdr = source[0].header
 
     # Get headerlet related keywords here
@@ -344,18 +343,18 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
         for extver in range(1, numext + 1):
             extn = (extname, extver)
             if 'SIPWCS' in extname and not active:
-                tab_extver = 0 # Since it has not been added to the SCI header yet
+                tab_extver = 0  # Since it has not been added to the SCI header yet
             else:
                 tab_extver = extver
             hdr = source[extn].header
-            if 'WCSNAME'+wcs_key in hdr:
+            if 'WCSNAME' + wcs_key in hdr:
                 wcsname = hdr['WCSNAME' + wcs_key]
             else:
                 wcsname = utils.build_default_wcsname(hdr['idctab'])
 
             selection = {'WCS_ID': wcsname, 'EXTVER': tab_extver,
-                         'SIPNAME':sipname, 'HDRNAME': hdrname,
-                         'NPOLNAME': npolname, 'D2IMNAME':d2imname
+                         'SIPNAME': sipname, 'HDRNAME': hdrname,
+                         'NPOLNAME': npolname, 'D2IMNAME': d2imname
                          }
 
             # Ensure that an entry for this WCS is not already in the dest
@@ -387,15 +386,14 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
                 # Interpret any 'pri.hdrname' or
                 # 'sci.crpix1' formatted keyword names
                 if '.' in fitkw:
-                    srchdr,fitkw = fitkw.split('.')
+                    srchdr, fitkw = fitkw.split('.')
                     if 'pri' in srchdr.lower(): srchdr = prihdr
                     else: srchdr = source[extn].header
                 else:
                     srchdr = source[extn].header
 
-                if fitkw+wcs_key in srchdr:
-                    new_table.data.field(key)[idx] = srchdr[fitkw+wcs_key]
-
+                if fitkw + wcs_key in srchdr:
+                    new_table.data.field(key)[idx] = srchdr[fitkw + wcs_key]
 
     # If idx was never incremented, no rows were added, so there's nothing else
     # to do...
@@ -403,16 +401,16 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
         return
 
     # Now, we need to merge this into the existing table
-    rowind = find_wcscorr_row(old_table.data, {'wcs_id':['','0.0']})
+    rowind = find_wcscorr_row(old_table.data, {'wcs_id': ['', '0.0']})
     old_nrows = np.where(rowind)[0][0]
     new_nrows = new_table.data.shape[0]
 
     # check to see if there is room for the new row
-    if (old_nrows + new_nrows) > old_table.data.shape[0]-1:
+    if (old_nrows + new_nrows) > old_table.data.shape[0] - 1:
         pad_rows = 2 * new_nrows
         # if not, create a new table with 'pad_rows' new empty rows
-        upd_table = fits.new_table(old_table.columns,header=old_table.header,
-                                     nrows=old_table.data.shape[0]+pad_rows)
+        upd_table = fits.new_table(old_table.columns, header=old_table.header,
+                                   nrows=old_table.data.shape[0] + pad_rows)
     else:
         upd_table = old_table
         pad_rows = 0
@@ -421,10 +419,10 @@ def update_wcscorr(dest, source=None, extname='SCI', wcs_id=None, active=True):
         if name in new_table.data.names:
             # reset the default values to ones specific to the row definitions
             for i in range(pad_rows):
-                upd_table.data.field(name)[old_nrows+i] = old_table.data.field(name)[-1]
+                upd_table.data.field(name)[old_nrows + i] = old_table.data.field(name)[-1]
             # Now populate with values from new table
             upd_table.data.field(name)[old_nrows:old_nrows + new_nrows] = \
-                    new_table.data.field(name)
+                new_table.data.field(name)
     upd_table.header['TROWS'] = old_nrows + new_nrows
 
     # replace old extension with newly updated table extension
@@ -447,14 +445,14 @@ def restore_file_from_wcscorr(image, id='OPUS', wcskey=''):
     wcs_table = fimg['WCSCORR']
     orig_rows = (wcs_table.data.field('WCS_ID') == 'OPUS')
     # create an HSTWCS object to figure out what WCS keywords need to be updated
-    wcsobj = stwcs.wcsutil.HSTWCS(fimg,ext=('sci',1))
+    wcsobj = stwcs.wcsutil.HSTWCS(fimg, ext=('sci', 1))
     wcshdr = wcsobj.wcs2header()
-    for extn in range(1,numsci+1):
+    for extn in range(1, numsci + 1):
         # find corresponding row from table
         ext_rows = (wcs_table.data.field('EXTVER') == extn)
-        erow = np.where(np.logical_and(ext_rows,orig_rows))[0][0]
+        erow = np.where(np.logical_and(ext_rows, orig_rows))[0][0]
         for key in wcshdr:
-            if key in wcs_table.data.names: # insure that keyword is column in table
+            if key in wcs_table.data.names:  # insure that keyword is column in table
                 tkey = key
 
                 if 'orient' in key.lower():
@@ -462,14 +460,14 @@ def restore_file_from_wcscorr(image, id='OPUS', wcskey=''):
                 if wcskey == '':
                     skey = key
                 else:
-                    skey = key[:7]+wcskey
-                fimg['sci',extn].header[skey] = wcs_table.data.field(tkey)[erow]
+                    skey = key[:7] + wcskey
+                fimg['sci', extn].header[skey] = wcs_table.data.field(tkey)[erow]
         for key in DEFAULT_PRI_KEYS:
             if key in wcs_table.data.names:
                 if wcskey == '':
                     pkey = key
                 else:
-                    pkey = key[:7]+wcskey
+                    pkey = key[: 7] + wcskey
                 fimg[0].header[pkey] = wcs_table.data.field(key)[erow]
 
     utils.updateNEXTENDKw(fimg)
@@ -498,25 +496,25 @@ def create_wcscorr(descrip=False, numrows=1, padding=0):
     def_float64_zeros = np.array([0.0] * trows, dtype=np.float64)
     def_float64_ones = def_float64_zeros + 1.0
     def_float_col = {'format': 'D', 'array': def_float64_zeros.copy()}
-    def_float1_col = {'format': 'D', 'array':def_float64_ones.copy()}
+    def_float1_col = {'format': 'D', 'array': def_float64_ones.copy()}
     def_str40_col = {'format': '40A',
                      'array': np.array([''] * trows, dtype='S40')}
     def_str24_col = {'format': '24A',
                      'array': np.array([''] * trows, dtype='S24')}
     def_int32_col = {'format': 'J',
-                     'array': np.array([0]*trows,dtype=np.int32)}
+                     'array': np.array([0] * trows, dtype=np.int32)}
 
     # If more columns are needed, simply add their definitions to this list
-    col_names = [('HDRNAME',  def_str24_col), ('SIPNAME',   def_str24_col),
-                 ('NPOLNAME', def_str24_col), ('D2IMNAME',  def_str24_col),
-                 ('CRVAL1',   def_float_col), ('CRVAL2',    def_float_col),
-                 ('CRPIX1',   def_float_col), ('CRPIX2',    def_float_col),
-                 ('CD1_1',    def_float_col), ('CD1_2',     def_float_col),
-                 ('CD2_1',    def_float_col), ('CD2_2',     def_float_col),
-                 ('CTYPE1',   def_str24_col), ('CTYPE2',    def_str24_col),
-                 ('ORIENTAT', def_float_col), ('PA_V3',     def_float_col),
-                 ('RMS_RA',   def_float_col), ('RMS_Dec',   def_float_col),
-                 ('NMatch',   def_int32_col), ('Catalog',   def_str40_col)]
+    col_names = [('HDRNAME', def_str24_col), ('SIPNAME', def_str24_col),
+                 ('NPOLNAME', def_str24_col), ('D2IMNAME', def_str24_col),
+                 ('CRVAL1', def_float_col), ('CRVAL2', def_float_col),
+                 ('CRPIX1', def_float_col), ('CRPIX2', def_float_col),
+                 ('CD1_1', def_float_col), ('CD1_2', def_float_col),
+                 ('CD2_1', def_float_col), ('CD2_2', def_float_col),
+                 ('CTYPE1', def_str24_col), ('CTYPE2', def_str24_col),
+                 ('ORIENTAT', def_float_col), ('PA_V3', def_float_col),
+                 ('RMS_RA', def_float_col), ('RMS_Dec', def_float_col),
+                 ('NMatch', def_int32_col), ('Catalog', def_str40_col)]
 
     # Define selector columns
     id_col = fits.Column(name='WCS_ID', format='40A',
@@ -529,7 +527,7 @@ def create_wcscorr(descrip=False, numrows=1, padding=0):
                              array=np.array(['O'] * numrows + [''] * padding,
                                             dtype='S'))
     # create list of remaining columns to be added to table
-    col_list = [id_col, extver_col, wcskey_col] # start with selector columns
+    col_list = [id_col, extver_col, wcskey_col]  # start with selector columns
 
     for c in col_names:
         cdef = copy.deepcopy(c[1])
@@ -552,7 +550,8 @@ def create_wcscorr(descrip=False, numrows=1, padding=0):
 
     return newtab
 
-def delete_wcscorr_row(wcstab,selections=None,rows=None):
+
+def delete_wcscorr_row(wcstab, selections=None, rows=None):
     """
     Sets all values in a specified row or set of rows to default values
 
@@ -588,7 +587,7 @@ def delete_wcscorr_row(wcstab,selections=None,rows=None):
             rowind = find_wcscorr_row(wcstab, selections=selections)
             delete_rows = np.where(rowind)[0].tolist()
     else:
-        if not isinstance(rows,list):
+        if not isinstance(rows, list):
             rows = [rows]
         delete_rows = rows
 
@@ -601,13 +600,14 @@ def delete_wcscorr_row(wcstab,selections=None,rows=None):
         return
 
     # identify next empty row
-    rowind = find_wcscorr_row(wcstab, selections={'wcs_id':['','0.0']})
+    rowind = find_wcscorr_row(wcstab, selections={'wcs_id': ['', '0.0']})
     last_blank_row = np.where(rowind)[0][-1]
 
     # copy values from blank row into user-specified rows
     for colname in wcstab.names:
         wcstab[colname][delete_rows] = wcstab[colname][last_blank_row]
 
+
 def update_wcscorr_column(wcstab, column, values, selections=None, rows=None):
     """
     Update the values in 'column' with 'values' for selected rows
@@ -645,7 +645,7 @@ def update_wcscorr_column(wcstab, column, values, selections=None, rows=None):
             rowind = find_wcscorr_row(wcstab, selections=selections)
             update_rows = np.where(rowind)[0].tolist()
     else:
-        if not isinstance(rows,list):
+        if not isinstance(rows, list):
             rows = [rows]
         update_rows = rows
 
@@ -654,8 +654,8 @@ def update_wcscorr_column(wcstab, column, values, selections=None, rows=None):
 
     # Expand single input value to apply to all selected rows
     if len(values) > 1 and len(values) < len(update_rows):
-        print('ERROR: Number of new values',len(values))
-        print('       does not match number of rows',len(update_rows),' to be updated!')
+        print('ERROR: Number of new values', len(values))
+        print('       does not match number of rows', len(update_rows), ' to be updated!')
         print('       Please enter either 1 value or the same number of values')
         print('       as there are rows to be updated.')
         print('    Table will not be updated...')
diff --git a/stwcs/wcsutil/wcsdiff.py b/stwcs/wcsutil/wcsdiff.py
index cfc2d66..9f00f1a 100644
--- a/stwcs/wcsutil/wcsdiff.py
+++ b/stwcs/wcsutil/wcsdiff.py
@@ -1,10 +1,12 @@
-from __future__ import print_function
+from __future__ import absolute_import, print_function
+
 from astropy import wcs as pywcs
 from collections import OrderedDict
 from astropy.io import fits
 from .headerlet import parse_filename
 import numpy as np
 
+
 def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
                      file2key=" ", verbose=False):
     """
@@ -48,28 +50,29 @@ def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
     sciobj, sciname, close_scifile = parse_filename(scifile)
     diff['file_names'] = [scifile, file2]
     if get_rootname(scifile) != get_rootname(file2):
-        #logger.info('Rootnames do not match.')
-        diff['rootname'] = ("%s: %s", "%s: %s") % (sciname, get_rootname(scifile), file2, get_rootname(file2))
+        # logger.info('Rootnames do not match.')
+        diff['rootname'] = ("%s: %s", "%s: %s") % (sciname, get_rootname(scifile), file2,
+                                                   get_rootname(file2))
         result = False
     for i, j in zip(sciextlist, fextlist):
         w1 = pywcs.WCS(sciobj[i].header, sciobj, key=scikey)
         w2 = pywcs.WCS(fobj[j].header, fobj, key=file2key)
         diff['extension'] = [get_extname_extnum(sciobj[i]), get_extname_extnum(fobj[j])]
         if not np.allclose(w1.wcs.crval, w2.wcs.crval, rtol=10**(-7)):
-            #logger.info('CRVALs do not match')
+            # logger.info('CRVALs do not match')
             diff['CRVAL'] = w1.wcs.crval, w2.wcs.crval
             result = False
         if not np.allclose(w1.wcs.crpix, w2.wcs.crpix, rtol=10**(-7)):
-            #logger.info('CRPIX do not match')
-            diff ['CRPIX'] = w1.wcs.crpix, w2.wcs.crpix
+            # logger.info('CRPIX do not match')
+            diff['CRPIX'] = w1.wcs.crpix, w2.wcs.crpix
             result = False
         if not np.allclose(w1.wcs.cd, w2.wcs.cd, rtol=10**(-7)):
-            #logger.info('CDs do not match')
-            diff ['CD'] = w1.wcs.cd, w2.wcs.cd
+            # logger.info('CDs do not match')
+            diff['CD'] = w1.wcs.cd, w2.wcs.cd
             result = False
         if not (np.array(w1.wcs.ctype) == np.array(w2.wcs.ctype)).all():
-            #logger.info('CTYPEs do not match')
-            diff ['CTYPE'] = w1.wcs.ctype,  w2.wcs.ctype
+            # logger.info('CTYPEs do not match')
+            diff['CTYPE'] = w1.wcs.ctype, w2.wcs.ctype
             result = False
         if w1.sip or w2.sip:
             if (w2.sip and not w1.sip) or (w1.sip and not w2.sip):
@@ -79,41 +82,41 @@ def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
                 diff['SIP_A'] = 'SIP_A differ'
                 result = False
             if not np.allclose(w1.sip.b, w2.sip.b, rtol=10**(-7)):
-                #logger.info('SIP coefficients do not match')
-                diff ['SIP_B'] = (w1.sip.b, w2.sip.b)
+                # logger.info('SIP coefficients do not match')
+                diff['SIP_B'] = (w1.sip.b, w2.sip.b)
                 result = False
         if w1.cpdis1 or w2.cpdis1:
             if w1.cpdis1 and not w2.cpdis1 or w2.cpdis1 and not w1.cpdis1:
                 diff['CPDIS1'] = "CPDIS1 missing"
-                result=False
+                result = False
             if w1.cpdis2 and not w2.cpdis2 or w2.cpdis2 and not w1.cpdis2:
                 diff['CPDIS2'] = "CPDIS2 missing"
                 result = False
             if not np.allclose(w1.cpdis1.data, w2.cpdis1.data, rtol=10**(-7)):
-                #logger.info('NPOL distortions do not match')
-                diff ['CPDIS1_data'] = (w1.cpdis1.data, w2.cpdis1.data)
+                # logger.info('NPOL distortions do not match')
+                diff['CPDIS1_data'] = (w1.cpdis1.data, w2.cpdis1.data)
                 result = False
             if not np.allclose(w1.cpdis2.data, w2.cpdis2.data, rtol=10**(-7)):
-                #logger.info('NPOL distortions do not match')
-                diff ['CPDIS2_data'] = (w1.cpdis2.data, w2.cpdis2.data)
+                # logger.info('NPOL distortions do not match')
+                diff['CPDIS2_data'] = (w1.cpdis2.data, w2.cpdis2.data)
                 result = False
         if w1.det2im1 or w2.det2im1:
             if w1.det2im1 and not w2.det2im1 or \
-                w2.det2im1 and not w1.det2im1:
+                    w2.det2im1 and not w1.det2im1:
                 diff['DET2IM'] = "Det2im1 missing"
                 result = False
             if not np.allclose(w1.det2im1.data, w2.det2im1.data, rtol=10**(-7)):
-                #logger.info('Det2Im corrections do not match')
-                diff ['D2IM1_data'] = (w1.det2im1.data, w2.det2im1.data)
-                result =  False
+                # logger.info('Det2Im corrections do not match')
+                diff['D2IM1_data'] = (w1.det2im1.data, w2.det2im1.data)
+                result = False
         if w1.det2im2 or w2.det2im2:
             if w1.det2im2 and not w2.det2im2 or \
                w2.det2im2 and not w1.det2im2:
                 diff['DET2IM2'] = "Det2im2 missing"
                 result = False
             if not np.allclose(w1.det2im2.data, w2.det2im2.data, rtol=10**(-7)):
-                #logger.info('Det2Im corrections do not match')
-                diff ['D2IM2_data'] = (w1.det2im2.data, w2.det2im2.data)
+                # logger.info('Det2Im corrections do not match')
+                diff['D2IM2_data'] = (w1.det2im2.data, w2.det2im2.data)
                 result = False
     if not result and verbose:
         for key in diff:
@@ -124,6 +127,7 @@ def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
         sciobj.close()
     return result, diff
 
+
 def get_rootname(fname):
     """
     Returns the value of ROOTNAME or DESTIM
@@ -139,12 +143,13 @@ def get_rootname(fname):
             rootname = fname
     return rootname
 
+
 def get_extname_extnum(ext):
     """
     Return (EXTNAME, EXTNUM) of a FITS extension
     """
     extname = ""
-    extnum=1
+    extnum = 1
     extname = ext.header.get('EXTNAME', extname)
     extnum = ext.header.get('EXTVER', extnum)
     return (extname, extnum)