More additions based on comments from Tim Peters, Neal Norwitz,

Gerhard Haring, and Guido van Rossum.

pep-0008.txt

@@ -500,9 +500,15 @@ Naming Conventions
       over class_ then just be consistent. :).
 
 
-Optimization and Other Programming Recommendations
+Programming Recommendations
 
-    - class-based exceptions are always preferred over string-based
+    - Comparisons to singletons like None should always be done with
+      'is' or 'is not'.  Also, beware of writing "if x" when you
+      really mean "if x is not None" -- e.g. when testing whether a
+      variable or argument that defaults to None was set to some other
+      value.
+
+    - Class-based exceptions are always preferred over string-based
       exceptions.  Modules or packages should define their own
       domain-specific base exception class, which should be subclassed
       from the built-in Exception class.  Always include a class
@@ -542,6 +548,14 @@ Optimization and Other Programming Recommendations
       sequences are false, so "if not seq" or "if seq" is preferable
       to "if len(seq)" or "if not len(seq)".
 
+    - Don't write string literals that rely on significant trailing
+      whitespace.  Such trailing whitespace is visually
+      indistinguishable and some editors (or more recently,
+      reindent.py) will trim them.
+
+    - Don't compare boolean values to True or False using == (bool
+      types are new in Python 2.3).
+
 
 References