Python与设计模式（一）——Abstract Factory

最近在重新学习Python，想找一些优秀的Python源代码阅读学习，加上前段时间一直在学习设计模式，所以选择了GitHub上这个项目作为学习对象：

https://github.com/faif/python-patterns

这里有用Python实现各个设计模式的源代码demo。

本篇从Abstract Factory开始介绍。

其源码如下：

#!/usr/bin/env python# -*- coding: utf-8 -*-# http://ginstrom.com/scribbles/2007/10/08/design-patterns-python-style/"""Implementation of the abstract factory pattern"""import siximport abcimport randomclass 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_factory    def 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 familydef get_factory():    """Let's be dynamic!"""    return random.choice([DogFactory, CatFactory])()# Implementation 2 of an abstract [e-mail]_metaclass(abc.ABCMeta)class Pet(object):    @classmethod    def from_name(cls, name):        for sub_cls in cls.__subclasses__():            if name == sub_cls.__name__.lower():                return sub_cls()    @abc.abstractmethod    def speak(self):        """"""class Kitty(Pet):    def speak(self):        return "Miao"class Duck(Pet):    def speak(self):        return "Quak"# Show pets with various factoriesif __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

代码对应的类图如下：

大家可能会感到奇怪：这里并没有抽象工厂啊？我们可以看这段代码：

# Create the proper familydef get_factory():    """Let's be dynamic!"""    return random.choice([DogFactory, CatFactory])()

这里，其实就实现了一个抽象工厂的功能，生成目标的factory。DogFactory用来生产Dog对象，CatFactory用来生产Cat对象。Dog类和Cat类都是Pet类的子类。