[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?

首先查看示例、PEP 696 的绑定规则、mypy 提交 fe15ee69b 以及所引用的 pyright issue。确定对泛型类进行 staticmethod 调用时约定的行为，并记录由此得出的规范决策，包括类型检查器应推断 Foo[int] 还是使用未知类型。