class Animal:
    def __init__(self, name):
        self.name = name

    def speak(self):
        print('~ ~ ~')


class Dog(Animal):
    def speak(self):
        print('汪汪汪')


class Cat(Animal):
    def speak(self):
        print('喵喵喵')


if __name__ == '__main__':
    animals = [Dog('spike'), Cat('tom'), Animal('jerry')]
    for animal in animals:
        animal.speak()