Typing with generic and inheritance

type_generic_inheritance.py

from typing import TypeVar, Optional, Generic, Protocol

class Additive(Protocol):
    def __add__(self: 'MyReturnType', other: 'MyReturnType') -> 'MyReturnType': ...

MyReturnType = TypeVar("MyReturnType", bound=Additive)

class Foo(Generic[MyReturnType]):

    def __init__(self, input: MyReturnType) -> None:
        self._input = input

    def concat(self, value: MyReturnType) -> MyReturnType:
        return self._input + value


f1 = Foo(2)
f1.concat(5)

f2 = Foo("ba")
f2.concat("glfkjh")

NewThing = TypeVar("NewThing", bound=Additive)

class Bar(Foo[NewThing], Generic[NewThing]):
    def bla(self):
        print(self._input)

f3 = Bar(2)
f3.concat(5)
f3.bla()

reveal_locals()
reveal_type(f3)