Shared via mypy Playground

main.py

from collections.abc import Callable

class Animal: ...
class Dog(Animal):
    def bark(self) -> None: print("woof")
class Cat(Animal): ...

class Handler[T]:
    def __init__(self, cb: Callable[[T], None]) -> None:
        self.cb = cb

def use(h: Handler[Dog]) -> None:
    h.cb = lambda d: d.bark()

ha = Handler[Animal](lambda a: print(a))
use(ha)       # mypy: no error (Handler[Animal] accepted as Handler[Dog])
ha.cb(Cat())  # Runtime: AttributeError: 'Cat' object has no attribute 'bark'