Allow inheriting from Self in TPS

[Peilonrayz (Peilonrayz)]

With the introduction of the Type Parameter Scope Self is(?) well defined in inheritance. I performed some tests (Pyright Playground) and all the typing features needed seem supported by Pyright. (Unlike mypy.)

Just like foo: ClassVar[T] works in Pyright (but errors per spec IIRC); could we allow class Foo(Iterable[Self]) to error but type correctly? The request is out-of-spec but to my uninformed eyes looks implementable with the existing features of Pyright.

[傅立业（Chris Fu） (Azureblade3808)]

See code --

from typing import Self

class Base[T]:
    def foo(self, /) -> T: ...

class Outer:
    class Inner(Base[Self]): ...

Assuming such usage of Self is allowed, what do you think the type of Outer.Inner().foo() should be? I believe the answer is Outer or even type[Outer] (Self in class context means the class itself) though you may disagree. So there is ambiguity.

[Peilonrayz (Peilonrayz)]

Can you argue against the point I'm making? None of the examples I created are nested classes and don't have the ambiguity you're constructing merely as a counter point. The Pyright solution is to use @class but bickering over the language construct ("@class") doesn't invalidate the normal usage of classes.

[Eric Traut (erictraut)]

It's not clear to me what problem you're trying to solve here. Perhaps if you start with the problem, we could suggest ways that you could solve it within the current type system.

If you'd like to propose changes to the type system, the Python Typing forum would be a more appropriate forum.

[Peilonrayz (Peilonrayz)]

I linked the Discussion in the OP. I'm not really sure what the OP or the linked OP don't explain.