GhH804 index names typehint

[loicdiridollou]

• Closes type annotation for Index/MultiIndex.names is incorrect #804
• Tests added: Please use assert_type() to assert the type of any return value

There remains the issue of mypy that complains once you set it as a tuple, it does not seem to recognize the expected type of the setter.

tests/test_indexes.py:1182: error: Incompatible types in assignment (expression has type "tuple[str]", variable has type "list[str | None]")  [assignment]
tests/test_indexes.py:1186: error: Incompatible types in assignment (expression has type "tuple[None]", variable has type "list[str | None]")  [assignment]

[Dr-Irv]

There remains the issue of mypy that complains once you set it as a tuple, it does not seem to recognize the expected type of the setter.

See python/mypy#3004 . Long standing issue (7+ years!!) in that mypy doesn't accept setters and getters on properties that have asymmetric arguments. Back in 2021, I was involved in a discussion on that issue with the pyright author and convinced him to support it.

So for this PR, I think you can just comment out the tests related to setting and getting tuples, and put a comment with a link to that mypy issue.

[loicdiridollou]

Thanks @Dr-Irv for the insight, will close this one for now. I have added the reference you provided to the issue.