Python doctests: test for None

Question

Using Python 2.7 I'm trying to test that the result of a particular function call is None

I would expect these tests to pass (excuse the rather silly example)

def six_or_none(val):     """     >>> six_or_none(6)     6     >>> six_or_none(4)     None     """     if val == 6:         return 6     return None 

However they yield the following result

Failed example:     six_or_none(4) Expected:     None Got nothing 

What's the correct way to test for None in doctests?

Answer 1

The Python interpreter ignores None return values, so doctests do the same.

Test for is None instead:

>>> six_or_none(4) is None True 

Answer 2

Other option would be a direct check for None:

def six_or_none(val):     """     >>> six_or_none(6)     6     >>> six_or_none(4)     """     if val == 6:         return 6     return None