Do not promote `None` as the first argument to `filter` in documentation.

[Chris Angelico]

On Wed, Mar 7, 2018 at 2:12 AM, Kirill Balunov <kirillbalunov at gmail.com> wrote:
>
>
> 2018-03-06 17:55 GMT+03:00 Chris Angelico <rosuav at gmail.com>:
>>
>> On Wed, Mar 7, 2018 at 1:48 AM, Kirill Balunov <kirillbalunov at gmail.com>
>> wrote:
>> > Note: For some historical reasons as the first argument you can use None
>> > instead of function, in this case the identity function is assumed. That
>> > is, all elements of iterable that are false are removed which is
>> > equivalent
>> > to (item for item in iterable if item). Currently, for the same purpose
>> > the
>> > preferred form is `filter(bool, iterable)`.
>> >
>>
>> I'd prefer to word it something like:
>>
>> If the first argument is None, the identity function is assumed. That
>> is, all elements of the iterable that are false are removed; it is
>> equivalent to (item for item in iterable if item). It is approximately
>> equivalent to (but faster than) filter(bool, iterable).
>>
>> ChrisA
>> --
>> https://mail.python.org/mailman/listinfo/python-list
>
>
> I do not want to seem rude and stubborn, but how much faster is it to
> highlight or emphasize it:
>

Timings mean little. Why do we write:

if lst:

instead of:

if bool(lst):

? Because it's unnecessary and pointless to call bool() on something
before using it in a boolean context. If that concept causes you
problems, it's not the fault of the filter function; filter simply
uses something in a boolean context.

So "the identity function" is more correct than "the bool() function".

ChrisA