Use _typeshed.NoneType for the type of None

[KotlinIsland]

Currently mypy uses a hardcoded type for NoneType, I think it should use the one from typeshed.

reveal_type(None.__bool__())  # note: Revealed type is "builtins.bool"

[erictraut]

This is defined correctly in typeshed.

@final
class NoneType:
    def __bool__(self) -> Literal[False]: ...

I'm not sure why mypy is revealing bool rather than Literal[False] in this case. Pyright reveals Literal[False] based on the above typeshed definition.

It's possible this was fixed recently in typeshed and mypy hasn't yet picked up the latest version.

[JelleZijlstra]

NoneType exists only in 3.10; I don't think mypy uses it to define None. It's hardcoded here instead: https://github.com/python/mypy/blob/master/mypy/checkmember.py#L319.

[erictraut]

NoneType has been defined in _typeshed.pyi for a while, and pyright uses its definition to avoid hardcoding assumptions. Mypy's logic probably predates that.

[KotlinIsland]

python/typeshed#6125

[KotlinIsland]

@JelleZijlstra I'm interested in getting mypy to use _typeshed.NoneType as the type of None, is this what you would want?

Where should I look, I can see that there is a mypy.types.NoneType.

I'm not sure how classes are represented, would this need to be replaced with a TypeInfo of _typeshed.NoneType?

[JelleZijlstra]

Yes, I think you'd have to replace mypy.types.NoneType. Honestly this seems like a lot of refactoring work for little reward.