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main.py

# mypy: no-strict-optional
from typing import overload, Protocol

class Descriptor:
    @overload
    def __get__(self, instance: None, owner: type) -> int: ...

    @overload
    def __get__(self, instance: object, owner: type) -> str: ...

    def __get__(self, instance: object | None, owner: type) -> int | str: ...

class A:
    prop = Descriptor()


x : int = A.prop
y : str = A().prop

a_or_none: A | None
z : str = a_or_none.prop