Add typing._SubscriptableSpecialForm and use it to fix various special forms - #7509

Thanks, but I agree with @JelleZijlstra that we need to be very careful with changes to typing. Personally, I'm open to #7508, as it seems to be solving an actual problem, and is a much smaller change. But this change is quite sweeping, and would require adding entries to the stubtest allowlists in order to propagate a lie in typeshed. I'm also not sure how much of a real problem it is that mypy thinks NoReturnand Never are subscriptable. (I suppose you could make more of an argument for TypeAlias or Self, but it still doesn't seem nearly as much of a problem as the typing.Union problem fixed in #7508.)

Fair enough 😀.

btw, why on earth is Self not subscriptable?

class Foo(Generic[T]):
    def foo(self) -> Self[int]: ...

Note that we reject using Self with type arguments, such as Self[int]. This is because it creates ambiguity about the type of the self parameter and introduces unnecessary complexity

pfff

Fair enough 😀.

btw, why on earth is Self not subscriptable?

class Foo(Generic[T]):
    def foo(self) -> Self[int]: ...

Note that we reject using Self with type arguments, such as Self[int]. This is because it creates ambiguity about the type of the self parameter and introduces unnecessary complexity

pfff

Ah, the dream of higher-kinded type variables