datetime supports non-int arguments

[sobolevn]

While discussing python/cpython#102791 I've noticed that datetime's objects can support non-int arguments:

>>> import datetime
>>> class Day:
...     def __index__(self):
...          return 1  # whatever
... 
>>> datetime.datetime(year=2023, month=3, day=Day())
datetime.datetime(2023, 3, 1, 0, 0)

Technically it might be used with some libs/dsls like datetime.datetime(year=Year(2023), month=Month(3), day=Day(2))

Should we use SupportsIndex there?

[srittau]

I am ok with supporting it here, since the various date classes explicitly check for it. But nothing I find particularly important, unless someone explicitly asks for it.

[AlexWaygood]

The proposed change SGTM too!

[sobolevn]

I confirm that __index__ is not an implementation detail here, it is a choice. Python's implementation also supports it: https://github.com/python/cpython/blob/7f760c2fca3dc5f46a518f5b7622783039bc8b7b/Lib/datetime.py#L518-L535

But, on the other hand: it is not documented and it is not tested.

So, I think we should keep this open. If some real use-case needs this, I will send a PR.
But, right now it is hypothetical (I've just seen this while reading CPython's source code).

[AlexWaygood]

Our policy is to prefer following the implementation rather than the documentation: https://github.com/python/typeshed/blob/main/CONTRIBUTING.md#what-to-do-when-a-projects-documentation-and-implementation-disagree

[sobolevn]

Ok, I will send a PR then 🚀

[sobolevn]

Resolved in #9915