[spec] Can staticmethod calls infer type parameters for the containing class?

In this code:

from typing import TypeVar, Generic
T = TypeVar('T')

class Foo(Generic[T]):
    @staticmethod
    def create(arg: T) -> 'Foo[T]':
        ...

reveal_type(Foo.create(1234))

What should the type be? Should T be inferred based on the argument to the static method, resulting in Foo[int]? Or should it be Foo[Unknown] or similar?

mypy (python/mypy@fe15ee69b) picks Foo[int].

pyright used to choose Foo[int], but microsoft/pyright#7454 changed it to pick Foo[Unknown], on the grounds that this is required to comply with PEP 696's statement:

Type parameter defaults should be bound by attribute access (including call and subscript).

My example does not include any type parameter defaults, but I can see the logic of applying the same rule without one: you wouldn't want it to be a breaking change to add a default.

Still, why can't these kinds of static method calls be treated like constructor calls, where class type parameters can be inferred from arguments?

Inizia esaminando l'esempio, le regole di binding di PEP 696, il commit di mypy fe15ee69b e la issue di pyright indicata. Determina il comportamento concordato per le chiamate a staticmethod sulle classi generiche e registra la decisione di specifica risultante, incluso se i type checker debbano inferire Foo[int] o usare un tipo sconosciuto.