"如何将类属性设置为类方法返回类型？"

Question

I got a class A who has a class method and take it's class property as return type.

# typings.py
from typing import TypeVar, Type

AType = TypeVar("AType", bound="A")

T = TypeVar("T", int, str)


class A:
    TYPE = int

    @classmethod
    def get_instance(cls: Type[AType]) -> "AType.TYPE":
        return cls.TYPE()


class B(A):
    TYPE = str


a = B.get_instance()

reveal_type(a)

Answer 1

Parameterise<\/em> over the TYPE<\/code> by making the class Generic<\/code> . This allows to refer to the class attribute TYPE<\/code> and the return type with the same type variable:

from typing import TypeVar, Type, Generic

T = TypeVar("T", str, int)


class Base(Generic[T]):
    TYPE: Type[T]

    @classmethod
    def get_instance(cls: "Type[Base[T]]") -> "T":
        return cls.TYPE()