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

[Kirill Balunov]

2018-03-06 16:51 GMT+03:00 Chris Angelico <rosuav at gmail.com>:

> On Wed, Mar 7, 2018 at 12:23 AM, Kirill Balunov <kirillbalunov at gmail.com>
> wrote:
> > Filter is generally faster than list comprehension or generators.
> >
> > %timeit [*filter(lambda x: x % 3, range(1000))]
> > 100 µs ± 16.4 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)
> >
> > f = lambda x: x % 3
> >
> > %timeit [*(f(i) for i in range(1000))]
> > 132 µs ± 73.5 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)
> >
> > %timeit [f(i) for i in range(1000)]
> > 107 µs ± 179 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)
> >
>
> These don't do the same thing, though. A more comparable comprehension is:
>
> [i for i in range(1000) if i % 3]
>
> rosuav at sikorsky:~$ python3 -m timeit '[i for i in range(1000) if i % 3]'
> 10000 loops, best of 5: 34.5 usec per loop
> rosuav at sikorsky:~$ python3 -m timeit '[*filter(lambda x: x % 3,
> range(1000))]'
> 5000 loops, best of 5: 81.1 usec per loop
>
> And my point about comprehensions was that you do NOT use a pointless
> function for them - you just have inline code. If there is a
> pre-existing function, sure! Use it. But when you use filter or map
> with a lambda function, you should probably use a comprehension
> instead.
>
> ChrisA
> --
> https://mail.python.org/mailman/listinfo/python-list
>

Thank you, I did not understand you at first, now everything is clear. In
this sense of `x % 3`, I fully agree with you.

With kind regards,
-gdg