工厂模式的本质就是用工厂方法代替new操作创建一种实例化对象的方式.

这里专门定义一个Operation类作为父类，加减乘除运算类继承Operation类，OperationFactory类用来决定什么时候创建对应的类

import random
from typing import Type


class Pet:
    def __init__(self, name: str) -> None:
        self.name = name

    def speak(self) -> None:
        raise NotImplementedError

    def __str__(self) -> str:
        raise NotImplementedError


class Dog(Pet):
    def speak(self) -> None:
        print("woof")

    def __str__(self) -> str:
        return f"Dog<{self.name}>"


class Cat(Pet):
    def speak(self) -> None:
        print("meow")

    def __str__(self) -> str:
        return f"Cat<{self.name}>"


class PetShop:

    """A pet shop"""

    def __init__(self, animal_factory: Type[Pet]) -> None:
        """pet_factory is our abstract factory.  We can set it at will."""

        self.pet_factory = animal_factory

    def buy_pet(self, name: str) -> Pet:
        """Creates and shows a pet using the abstract factory"""

        pet = self.pet_factory(name)
        print(f"Here is your lovely {pet}")
        return pet


# Additional factories:

# Create a random animal
def random_animal(name: str) -> Pet:
    """Let's be dynamic!"""
    return random.choice([Dog, Cat])(name)


if __name__ == '__main__':
    cat_shop = PetShop(Cat)
    pet = cat_shop.buy_pet("Lucy")
    pet.speak()

    shop = PetShop(random_animal)
    for name in ["Max", "Jack", "Buddy"]:
        pet = shop.buy_pet(name)
        pet.speak()
        print("=" * 20)