All code referred to is from bltinmodule.c, Python 2.7.8:
https://github.com/python/cpython/blob/2.7/Python/bltinmodule.c

filter implements and optimization for PyBool_Type, making it equivalent to PyNone:

    # Line 303
    if (func == (PyObject *)&PyBool_Type || func == Py_None)

The specializations for tuples, byte strings and unicode don't have this:

    # Lines 2776, 2827, 2956, 2976
    if (func == Py_None)

This is a damper against recommending `filter(bool, ...)`.

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Python 3 of course does not have these specializations, so has no bug.

Is there code that isn't working as documented or are you asking for additional optimizations to make the other cases run a bit faster when 'bool' is passed in as the filter function?

It's solely a speed thing. I think it was an oversight that the optimisation was only applied to lists. I didn't expect the optimisation to break when applied to tuples.

It is a bit late in the game for 2.7 micro-optimizations.

FWIW, I don't think these weren't oversights. There isn't really much of a use case for the bool filter for strings and unicode inputs.  And the case of tuple inputs isn't used much ("lists are for looping/filtering and tuples are like records in a DB or structs in C").

Since there is no bug here and we're trying to touch 2.7 as little as possible these days, I recommend closing as "not a bug" or "won't fix".

If optimizing uncommon cases is important for you, then just use "filter(None, iterable)" instead of "filter(bool, iterable)" or work with itertools.ifilter() and itertools.ifilterfalse().

That sounds OK to me. It's a bit of a non-issue once you know about it.