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

[Jason Friedman]

On Tue, Mar 6, 2018 at 1:52 AM, Kirill Balunov <kirillbalunov at gmail.com>
wrote:

>
> I propose to delete all references in the `filter` documentation that the
> first argument can be `None`, with possible depreciation of `None` as the
> the first argument - FutureWarning in Python 3.8+ and deleting this option
> in Python 4. Personally, regarding the last point - depreciation, I do not
> see this as a great necessity, but I do not find that the option with
> `None`
> should be offered and suggested through the documentation. Instead, it is
> better to show an example with using `filter(bool, iterable)` which is
> absolutely
> equivalent, more readable, but a little bit slower.
>
> Currently documentation for `None` case uses `identity function is
> assumed`, what is this `identity` and how it is consistent with
> truthfulness?
>
> In addition, this change makes the perception of `map` and `filter` more
> consistent,with the rule that first argument must be `callable`.
>
> I see only one moment with `None`, since `None` is a keyword, the behavior
> of `filter(None, iterable)` is alsways guaranteed, but with `bool` it is
> not. Nevertheless, we are all adults here.
>

I won't pretend I am qualified to debate the technical aspects here, but
regarding this snippet:

... Instead, it is better to show an example with using `filter(bool,
iterable)` which is absolutely equivalent, more readable ...

as a ordinary Python user I'd be interested in improvements to the
documentation, including suggestions on real-world usage.  For example,
Chris Angelico below says in part:

... that said, though, any use of filter() that involves a lambda
function should
probably become list comps or genexps, so filter itself should only be used
when ...

Kirill, taking deprecation/removal off the table, what changes would you
recommend to the documentation?