[Python-ideas] "Exposing" `__min__` and `__max__`

[James Edwards]

>
>    I'd want to see code that currently uses ``if isinstance`` to switch
> between ``max(x)`` and ``x.max()``.


I understand that, and I've spent a few hours searching github with
less-than-stellar results due to github's search syntax ignoring '.' and '('
<https://help.github.com/articles/searching-code/#considerations-for-code-search>.
(That being said, there are a number of projects
<https://github.com/search?l=Python&q=__min__&type=Code> on github that
seem to expect __min__ to work (example
<https://github.com/windowssocket/algorithm/blob/d731dca2917b6d6073a49d53cf4376b75da7e0c7/binarysearchtree.py>),
but it's true that some are using the dunder for their own purposes.).

However, there are many modules that implement objects that could make good
use of exposing __min__ (e.g. bintrees <https://pypi.org/project/bintrees/>,
sortedcontainers <http://www.grantjenks.com/docs/sortedcontainers/>).

bintrees provides `min_item()` and `max_item()` accessors.
sortedcontainers doesn't seem to explicitly provide similar methods, but
maintain the sortedness of the objects so min and max can be accessed via
index.

And I can't stress enough the value in being able to switch to one of these
classes from a standard iterable and have the rest of your code (e.g.
`min()`s "just work").

Also, the desire for custom implementations is there
<https://stackoverflow.com/questions/45308212/is-there-a-way-to-return-a-custom-value-for-min-and-max-in-python>,
but the proposed solutions rely on (IMO) ugly hacks that would break other
things.

The search for the perfect `x.min() if isinstance(...) else min(x)` still
continues, however.



On Wed, Jun 27, 2018 at 11:30 AM, Michael Selik <mike at selik.org> wrote:

> On Wed, Jun 27, 2018 at 8:16 AM Franklin? Lee <
> leewangzhong+python at gmail.com> wrote:
>
>> On Wed, Jun 27, 2018, 10:31 Steven D'Aprano <steve at pearwood.info> wrote:
>>
>>> On Wed, Jun 27, 2018 at 06:52:14AM -0700, Michael Selik wrote:
>>> > My intent was to ask where a range was in fact passed into max, not
>>> merely
>>> > where it could be. It'd be enlightening to see a complete, realistic
>>> > example.
>>>
>>> A complete, realistic example is as I said: you call max() on some
>>> object which you don't control, the caller does. You could be
>>> passed a list, or a set, or a bitset, a binary search tree, a range
>>> object, whatever the caller happens to pass to you.
>>>
>>
>> Let's just assume Michael wants to know, and isn't making an argument
>> against the proposal.
>>
>
> I do want to know, but it's also an argument against the proposal -- that
> no one has contributed in-context usage to demonstrate the value. I'd want
> to see code that currently uses ``if isinstance`` to switch between
> ``max(x)`` and ``x.max()``. Chris Barker explained the issue well.
>
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