Sebastian Rittau

I think a good middle ground to try first would be to change the `__key` in what is not the second and third overload to `_KT | None`. This should...

Considering that `deque` doesn't derive from `(Mutable)Sequence` at runtime, we should at least try to remove that base class. This might be too disruptive, but an exploratory PR would be...

Thanks, it makes sense to me to use a classifier here. The [documentation for pyproject.toml](https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license) says to use of the license classifiers from the [classifiers list](https://pypi.org/classifiers/) (minus the prefix). But...

I don't think we should use classifiers that contradict the official documentation. It's great to see that there's some progress to improve the license situation, but I'd prefer to wait...

> I am not very familiar with packaging arcana, but I'd prefer to avoid relying on any unspecified behavior, and instead use PEP 639 now that it's been provisionally accepted....

Or python/typing#566, which would replace this with `AnyOf[X, None]` and could also be controlled with strictness flags.

@JelleZijlstra Since you've already fixed some problem, do you want to close the remaining problems (`__init__` -> `__new__`)? Otherwise I would close this PR.

This looks completely reasonable to me, suspiciously so, in fact. And the primer hits seem to agree, although I haven't looked at the "red" hits in detail. I wonder whether...

> Closing as I don't think this makes mypy more useful. In the long term we should get rid of `builtins.function` from the stub (and I would recommend all type...

> No, I don't need them, I just want to start actively contributing to this project, because I'm interested in typing. Ok, could you remove them for now? This makes...