The Little Book of Python Anti-Patterns

Although I mostly agree with "Returning more than one variable type from function call," I do have some disagreement.

On the restriction itself, I'm fine with returning, for example, any kind of iterable, whether it's a list, tuple, string or whatever. It depends on context, and python is very much an interface/context kind of language.

As for the anti-example given, that code would not fail in most print contexts:

  In [1]: a = None

  In [2]: print a
  None

A better anti-example might have been:

  In [3]: for i in a:
     ...:     print i
     ...:     
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  <ipython-input-3-6fc9adb94b0c> in <module>()
  ----> 1 for i in a:
        2     print i
        3 
  
  TypeError: 'NoneType' object is not iterable

Chapter performance, use set instead list: If you convert a complete list to a set only to check if a values in a list this is not performant. Use list.index or binary search instead. But for every performance example you should offer a micro benchmark example.

Second comment: Would you switch to python3 syntax or annotate the examples with python2/python3 differences?