Python: type-hinting a classmethod that returns an instance of the class, for a class that is inherited

For an example of how to apply Brian’s answer:

• with a TypeVar:

from typing import TypeVar


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


class A:

    def __init__(self):
        print("A")
        self.hello = "hello"

    @classmethod
    def bobo(cls: type[AnyA]) -> AnyA:
        return cls()

class B(A):

    def __init__(self):
        print("B")
        super().__init__()
        self.world = "world"

reveal_type(B.bobo())  # B

• with Self:

from typing import Self

class A:

    def __init__(self):
        print("A")
        self.hello = "hello"

    @classmethod
    def bobo(cls) -> Self:
        return cls()

class B(A):

    def __init__(self):
        print("B")
        super().__init__()
        self.world = "world"

reveal_type(B.bobo())  # B

If your version of Python doesn’t have Self yet, you can use the typing-extensions package, which serves as backport for some typing features:

- from typing import Self
+ from typing_extensions import Self