class Pets:
    subclasses = []

    def __init_subclass__(cls, **kwargs):
        super().__init_subclass__(**kwargs)
        cls.subclasses.append(cls)

class Dog(Pets):
    def speak(self):
        print("woof")

class Cat(Pets):
    def speak(self):
        print("meow")


doggo = Dog()
doggo.speak()
cat = Cat()
cat.speak()
my_pets = Pets()
my_pets.subclasses