contextvars.Context doesn't inherit from Mapping

[tungol]

It's not a subclass, it's not registered to Mapping, and Mapping isn't protocol-like, so at runtime:

>>> issubclass(Context, Mapping)
False

It does have all the necessary methods to be Mapping, it just isn't.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[AlexWaygood]

That's kind of interesting that we don't do the collections.abc.Mapping.register(Context) thing at runtime; feels like an omission over at CPython

[srittau]

Interesting, but the primer hits are encouraging.

[tungol]

Yeah, I was wondering if maybe the right thing to do here was add the registration to cpython?

I haven't looked at them in detail yet, but two others in a somewhat similar boat are multiprocessing.managers.DictProxy and multiprocessing.managers.BaseListProxy. They're MutableMapping and MutableSequence in typeshed, respectively, but neither is actually registered to the ABC at runtime. They're on my "investigate" list coming up.

[AlexWaygood]

Yeah, I was wondering if maybe the right thing to do here was add the registration to cpython?

Very possibly. In theory of course, we could do this change and the CPython change, though it might lead to some annoying branching in the stubs if the CPython change is only accepted for Python 3.14+

[tungol]

This is now fixed in cpython for 3.12 and up. It probably doesn't make sense to branch for the sake of 3.8 to 3.11.