Python doctests: test for None

doctest, python

Solution

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

Test for `is None` instead:

>>> six_or_none(4) is None
True

Problem

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?

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