How to annotate class Methods to return only instances of their class or subclass in python

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1

I have a class method that can return the instance of its class or subclass (depending on the
arguments), but not instance of the supertype.

How to add annotations here?

from typing import *


class A:
    @classmethod
    def meth(cls):  # Type annotation here
        # Can return instance of A, B or C class
        ...


class B(A):
    @classmethod
    @override
    def meth(cls):  # Type annotation here
        # Can return instance of B or C class, but not A
        ...


class C(B):
    @classmethod
    @override
    def meth(cls):  # Type annotation here
        # Can return only instance of C
        ...

I know that I can just add -> 'A', -> 'B', -> 'C' annotations to these methods, but this class is intended for subclassing by library user, I need to force user’s subclasses to be annotated to return only subclasses of them.

2

Is this a duplicate?

3

Duplicate of Return type Self: returning subclass - #5 by t1m013y

4

Re-asked this because Return type Self: returning subclass - #5 by t1m013y was about how does typing.Self work and this is about how to make what I was thinking typing.Self does.

6

Then these methods should all be annotated to return typing.Self – that’s exactly what it enforces. Which makes this a duplicate of the other thread.