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Python与设计模式(一)——Abstract Factory

2017-09-19 17:19 274 查看
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 six
import abc
import random

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_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 makes

class 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 classes

class 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])()

# Implementation 2 of an abstract factory
@six.add_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 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
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 family
def 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。
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标签:  python 设计模式