[Python-Dev] itertools predicates

[Francisco Couzo]

Some functions that take a predicate from itertools accept None as its
predicate:

>>> list(itertools.filterfalse(None, range(10)))
[0]
>>> list(itertools.groupby([0,0,1,1], None))
[(0, <itertools._grouper object at 0x7fedc2047198>), (1,
<itertools._grouper object at 0x7fedc2
0471d0>)]

While others don't:

>>> list(itertools.dropwhile(None, range(10)))
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable

I'd be interested in writing a patch to make itertools more consistent if
there's a consensus.

I see two possible solutions:

   - Either remove None as a predicate parameter, which would not be
   backwards compatible.
   - Or make the functions that don't accept None start accepting it.
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