Abstract Factory（抽象工厂）

意图：

提供一个创建一系列相关或相互依赖对象的接口，而无需指定它们具体的类。 
适用性：

一个系统要独立于它的产品的创建、组合和表示时。

一个系统要由多个产品系列中的一个来配置时。

当你要强调一系列相关的产品对象的设计以便进行联合使用时。

当你提供一个产品类库，而只想显示它们的接口而不是实现时。

#!/usr/bin/python
#coding:utf8
'''
Abstract Factory
'''

import random

class PetShop:
    """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("This is a lovely", str(pet))
        print("It says", pet.speak())
        print("It eats", self.pet_factory.get_food())

# Stuff that our factory makes

class Dog:
    def speak(self):
        return "woof"

    def __str__(self):
        return "Dog"

class Cat:
    def speak(self):
        return "meow"

    def __str__(self):
        return "Cat"

# Factory classes

class DogFactory:
    def get_pet(self):
        return Dog()

    def get_food(self):
        return "dog food"

class CatFactory:
    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])()

# Show pets with various factories
if __name__ == "__main__":
    shop = PetShop()
    for i in range(3):
        shop.pet_factory = get_factory()
        shop.show_pet()
        print("=" * 20)