零、建造者模式

• 什么是建造者模式
  使用多个简单的对象一步一步构建成一个复杂的对象。这种类型的设计模式属于建造者模式，它提供了一种创建对象的最佳方式，将一个复杂对象的构造过程与其表象分离，同一个构造过程可用于创建多个不同的表现。

一、身边的例子

• 麦当劳
  麦当劳的汉堡套餐种类有很多（如：汉堡+可乐、汉堡+薯条、汉堡+可乐+薯条），顾客在购买的时候关注的是套餐的种类（表现），而不关注套餐制作的过程（建造过程）。在这里顾客就是客户端，收银员就是指挥者，后厨人员就是建造者。
• django-widgy
  django-widgy是Django的第三方编辑器扩展，可以构建不同风格的HTML代码。

二、什么情况下使用

创建一个由多个部分构成的对象，而且它的构成需要一步接一步地完成，只有当各个部分都创建好后，这个对象才算创建完成。

三、应用案例

以下代码，通过订购两种不同口味的比萨并，来进一步学习建造者模式

import time
from enum import EnumPizzaProgress = Enum('PizzaProgress', 'queued preparation baking ready')
PizzaDough = Enum('PizzaDough', 'thin thick')
PizzaSauce = Enum('PizzaSauce', 'tomato creme_fraiche')
PizzaTopping = Enum('PizzaTopping', 'mozzarella double_mozzarella bacon ham mushrooms red_onion oregano')
STEP_DELAY = 3class Pizza:'''最终产品类'''def __init__(self, name):self.name = nameself.dough = Noneself.sauce = Noneself.topping = []def __str__(self):return self.namedef prepare_dough(self, dough):self.dough = doughprint('preparing the {} dough of you {}...'.format(self.dough.name, self))time.sleep(STEP_DELAY)print('done with the {} dough'.format(self.dough.name))class CreamyBaconBuilder:"""奶油熏肉比萨建造者"""def __init__(self):self.pizza = Pizza('creamy bacon')self.progress = PizzaProgress.queued# 烤制时间self.baking_time = 7# 生面团def prepare_dough(self):self.progress = PizzaProgress.preparationself.pizza.prepare_dough(PizzaDough.thin)# 添加沙司def add_sauce(self):print('adding the creme fraiche sauce to your creamy bacon')self.pizza.sauce = PizzaSauce.Creme_fraiche# 暂停3秒，模拟制作的时间time.sleep(STEP_DELAY)print('done with the creme fraiche sauce')# 添加各种配料def add_topping(self):print('adding the topping (mozzarella,bacon,ham,mushrooms,red onion,oregano) to your creamy bacon')self.pizza.topping.append([t for t in (PizzaTopping.mozzarella, PizzaTopping.bacon, PizzaTopping.ham, PizzaTopping.mushrooms,PizzaTopping.red_onion, PizzaTopping.oregano)])time.sleep(STEP_DELAY)print('done with the topping (mozzarella,bacon,ham,mushrooms,red onion, oregano)')# 烤比萨def bake(self):self.progress = PizzaProgress.bakingprint('baking your creamy bacon for {} seconds'.format(self.baking_time))time.sleep(self.baking_time)self.progress = PizzaProgress.readyprint('your creamy bacon is ready')class MargaritaBuilder:'''玛格丽特比萨建造者'''def __init__(self):self.pizza = Pizza('margarita')self.progress = PizzaProgress.queuedself.baking_time = 5def prepare_dough(self):self.progress = PizzaProgress.preparationself.pizza.prepare_dough(PizzaDough.thin)def add_sauce(self):print('adding the tomato sauce to your margarita...')self.pizza.sauce = PizzaSauce.tomatotime.sleep(STEP_DELAY)print('done with the tomato sauce')def add_topping(self):print('adding the topping (double mozzarella, oregano) to your margarita')self.pizza.topping.append([i for i in (PizzaTopping.double_mozzarella, PizzaTopping.oregano)])time.sleep(STEP_DELAY)print('done with the topping (double mozzarrella,oregano)')def bake(self):self.progress = PizzaProgress.bakingprint('baking your margarita for {} seconds'.format(self.baking_time))time.sleep(self.baking_time)self.progress = PizzaProgress.readyprint('your margarita is ready')class Waiter:'''服务员（指挥者）'''def __init__(self):self.builder = Nonedef construct_pizza(self, builder):self.builder = builder[step() for step in (builder.prepare_dough, builder.add_sauce, builder.add_topping, builder.bake)]@propertydef pizza(self):return self.builder.pizzadef validate_style(builders):'''验证输入类'''try:pizza_style = input('What pizza would you like ,[m]argarita or [c]reamy bacon?')builder = builders[pizza_style]()vaild_input = Trueexcept KeyError as err:print('Sorry,only margarita (key m) and creamy bacon (key c) are availabke')return (False, None)return (True, builder)def main():builders = dict(m=MargaritaBuilder, c=CreamyBaconBuilder)valid_input = Falsewhile not valid_input:valid_input, builder = validate_style(builders)waiter = Waiter()waiter.construct_pizza(builder)pizza = waiter.pizzaprint('Enjoy your  {}!'.format(pizza))if __name__ == '__main__':main()