diff --git a/png.py b/png.py
index ac17ad7..331f341 100644
--- a/png.py
+++ b/png.py
@@ -167,7 +167,7 @@ from __future__ import generators
 __version__ = "$URL: http://pypng.googlecode.com/svn/trunk/code/png.py $ $Rev: 201 $"
 
 from array import array
-try: # See :pyver:old
+try:  # See :pyver:old
     import itertools
 except:
     pass
@@ -314,7 +314,7 @@ class Writer:
                  gamma=None,
                  compression=None,
                  interlace=False,
-                 bytes_per_sample=None, # deprecated
+                 bytes_per_sample=None,  # deprecated
                  planes=None,
                  colormap=None,
                  maxval=None,
@@ -1006,7 +1006,7 @@ def filter_scanline(type, line, fo, prev=None):
             ai += 1
     def paeth():
         # http://www.w3.org/TR/PNG/#9Filter-type-4-Paeth
-        ai = -fo # also used for ci
+        ai = -fo  # also used for ci
         for i, x in enumerate(line):
             a = 0
             b = prev[i]
@@ -1033,11 +1033,11 @@ def filter_scanline(type, line, fo, prev=None):
         # of the image simpler.  "up" becomes "none"; "paeth" becomes
         # "left" (non-trivial, but true). "average" needs to be handled
         # specially.
-        if type == 2: # "up"
-            return line # type = 0
+        if type == 2:  # "up"
+            return line  # type = 0
         elif type == 3:
             prev = [0] * len(line)
-        elif type == 4: # "paeth"
+        elif type == 4:  # "paeth"
             type = 1
     if type == 0:
         out.extend(line)
@@ -1047,7 +1047,7 @@ def filter_scanline(type, line, fo, prev=None):
         up()
     elif type == 3:
         average()
-    else: # type == 4
+    else:  # type == 4
         paeth()
     return out
 
@@ -1786,7 +1786,7 @@ class Reader:
                     row = group(row, planes)
                     opa = map(it.__ne__, row)
                     opa = map(maxval.__mul__, opa)
-                    opa = zip(opa) # convert to 1-tuples
+                    opa = zip(opa)  # convert to 1-tuples
                     yield array(typecode,
                       itertools.chain(*map(operator.add, row, opa)))
             pixels = itertrns(pixels)