> Comment: This rule applies to special methods like __getitem__
> and __setitem__. 'lis.append(item)' is equivalent to
> lis.__setitem__(len(lis):len(lis), item), so it should not be so
> surprising that it has the same return.

It's not true for all special methods.  __iadd__ and __imul__ return the list itself.

That's a minor nitpick though.  +1 on adding "and return None" to the docstrings of methods that often trip people up.  Not everyone will read them, but some people will.