设计模式-抽象工厂模式-abstractfactory-python

def

为创建一组相关或相互依赖的对象提供一个接口， 而且无须指定它们的具体类。

usage

● 封装性。每个产品的实现类不是高层模块要关心的， 只要知道工厂类是谁， 我就
能创建出一个需要的对象， 省时省力， 优秀设计就应该如此。

● 产品族内的约束为非公开状态。 生产过程对调用工厂类的高层模块来说是透明的， 它不需要知道这个约束， 具体的产品族内的约束是在工厂内实现的。

attention

抽象工厂模式的最大缺点就是产品族扩展非常困难。

抽象工厂模式的使用场景定义非常简单： 一个对象族（或是一组没有任何关系的对象）都有相同的约束， 则可以使用抽象工厂模式。

code

class PetShop(object):"""A pet shop"""def __init__(self, animal_factory=None):"""pet_factory is our abstract factory.  We can set it at will."""self.pet_factory = animal_factorydef show_pet(self):"""Creates and shows a pet using the abstract factory"""pet = self.pet_factory.get_pet()print("We have a lovely {}".format(pet))print("It says {}".format(pet.speak()))print("We also have {}".format(self.pet_factory.get_food()))# Stuff that our factory makesclass Dog(object):def speak(self):return "woof"def __str__(self):return "Dog"class Cat(object):def speak(self):return "meow"def __str__(self):return "Cat"# Factory classesclass DogFactory(object):def get_pet(self):return Dog()def get_food(self):return "dog food"class CatFactory(object):def get_pet(self):return Cat()def get_food(self):return "cat food"# Create the proper family
def get_factory():"""Let's be dynamic!"""return random.choice([DogFactory, CatFactory])()# 抽象工厂在这里！！！
@six.add_metaclass(abc.ABCMeta)
class Pet(object):@classmethoddef from_name(cls, name):for sub_cls in cls.__subclasses__():if name == sub_cls.__name__.lower():return sub_cls()@abc.abstractmethoddef speak(self):""""""class Kitty(Pet):def speak(self):return "Miao"class Duck(Pet):def speak(self):return "Quak"# Show pets with various factories
if __name__ == "__main__":for i in range(3):shop = PetShop(get_factory())shop.show_pet()print("=" * 20)for name0 in ["kitty", "duck"]:pet = Pet.from_name(name0)print("{}: {}".format(name0, pet.speak()))### OUTPUT ###
# We have a lovely Cat
# It says meow
# We also have cat food
# ====================
# We have a lovely Dog
# It says woof
# We also have dog food
# ====================
# We have a lovely Cat
# It says meow
# We also have cat food
# ====================
# kitty: Miao
# duck: Quak

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