Fix several mypy errors when run on the 3.11 stdlib

[AlexWaygood]

If you apply @hauntsaninja's patch to mypy_test.py in python/mypy#12220, here is the output when running python tests/mypy_test.py -p3.11 on the master branch (using Python 3.10, mypy 0.931):

stdlib\typing.pyi:1166: error: Variable "typing.Never" is not valid as a type  [valid-type]
stdlib\typing.pyi:1166: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
stdlib\builtins.pyi:1713: error: Value of type "Type[type]" is not indexable  [index]
stdlib\builtins.pyi:1721: error: Variable "builtins._SplitCondition" is not valid as a type  [valid-type]
stdlib\builtins.pyi:1721: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
stdlib\builtins.pyi:1722: error: Variable "builtins._SplitCondition" is not valid as a type  [valid-type]
stdlib\builtins.pyi:1722: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
stdlib\enum.pyi:141: error: Decorated property not supported  [misc]
stdlib\enum.pyi:143: error: Decorated property not supported  [misc]
stdlib\enum.pyi:172: error: Decorated property not supported  [misc]
stdlib\enum.pyi:192: error: Signature of "value" incompatible with supertype "Flag"  [override]
stdlib\enum.pyi:203: error: Decorated property not supported  [misc]
stdlib\enum.pyi:205: error: Decorated property not supported  [misc]
stdlib\enum.pyi:233: error: Decorated property not supported  [misc]
stdlib\enum.pyi:236: error: Cannot inherit from final class "StrEnum"  [misc]
stdlib\enum.pyi:248: error: Cannot inherit from final class "StrEnum"  [misc]
stdlib\asyncio\base_events.pyi:301: error: Signature of "create_datagram_endpoint" incompatible with supertype "AbstractEventLoop"  [override]
stdlib\asyncio\base_events.pyi:301: note:      Superclass:
stdlib\asyncio\base_events.pyi:301: note:          def [_ProtocolT <: BaseProtocol] create_datagram_endpoint(self, protocol_factory: Callable[[], _ProtocolT], local_addr: Optional[Tuple[str, int]] = ..., remote_addr: Optional[Tuple[str, int]] = ..., *, family: int = ..., proto: int = ..., flags: int = ..., reuse_address: Optional[bool] = ..., reuse_port: Optional[bool] = ..., allow_broadcast: Optional[bool] = ..., sock: Optional[socket] = ...) -> Coroutine[Any, Any, Tuple[BaseTransport, _ProtocolT]]
stdlib\asyncio\base_events.pyi:301: note:      Subclass:
stdlib\asyncio\base_events.pyi:301: note:          def [_ProtocolT <: BaseProtocol] create_datagram_endpoint(self, protocol_factory: Callable[[], _ProtocolT], local_addr: Optional[Tuple[str, int]] = ..., remote_addr: Optional[Tuple[str, int]] = ..., *, family: int = ..., proto: int = ..., flags: int = ..., reuse_port: Optional[bool] = ..., allow_broadcast: Optional[bool] = ..., sock: Optional[socket] = ...) -> Coroutine[Any, Any, Tuple[BaseTransport, _ProtocolT]]

Here is the output when running python tests/mypy_test.py -p3.11 with this patch applied:

stdlib\typing.pyi:1166: error: Variable "typing.Never" is not valid as a type  [valid-type]
stdlib\typing.pyi:1166: note: See https://mypy.readthedocs.io/en/stable/common_issues.html#variables-vs-type-aliases
stdlib\enum.pyi:222: error: Cannot inherit from final class "StrEnum"  [misc]
stdlib\enum.pyi:234: error: Cannot inherit from final class "StrEnum"  [misc]

[github-actions]

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

[JelleZijlstra]

Thanks! Are the Never errors with mypy master or the latest release?

And the StrEnum errors seem like a mypy bug, do you know if it's already tracked?

[AlexWaygood]

Thanks! Are the Never errors with mypy master or the latest release?

With the latest release (0.931); I assume (though I haven't checked) that python/mypy#12153 fixes them. I'll try running the same test with mypy master and get back to you.

And the StrEnum errors seem like a mypy bug, do you know if it's already tracked?

It's been raised in python/mypy#12220

[AlexWaygood]

Okay, if I run mypy_test.py -p3.11 using mypy master, the Never errors and the StrEnum errors go away. There is however this new error, which also seems like a mypy bug:

stdlib\enum.pyi:172: error: Only a single data type mixin is allowed for Enum subtypes, found extra "enum.ReprEnum"  [misc]
stdlib\enum.pyi:213: error: Only a single data type mixin is allowed for Enum subtypes, found extra "enum.ReprEnum"  [misc]

I've filed an issue over at mypy: python/mypy#12258