建造者模式

想要创建一个由多个部分构成的对象，而且他的构成需要一步接一步地完成。只有当各个部分都创建好，这个对象才是完整的。这时就需要建造者模式

建造者设计模式：将一个复杂对象的构造过程与其表现分离，构造过程可用于创建多个不同的表现。

该模式中有两个参与者：建造者和指挥者

建造者负责创建复杂对象的各个组成部分。

指挥者使用建造者实例控制建造的过程。

建造者模式与工厂模式的区别

1.工厂模式以单个步骤创建对象，而建造者模式以多个步骤创建独享，并且几乎始终使用同一个指挥者；

2.在工厂模式下，会立即返回一个创建好的对象；而在建造者模式下，仅在需要时客户端代码才显示地请求指挥者返回最终的对象。

其实在django-widgy中建造者模式就得到了实际应用。django-widgy是一个Django的第三方树编辑器扩展，可用作内容管理系统（Content Management System, CMS）。它包含一个网页构建器，用在创建不同布局的HTML页面。

1. 建造者模式的苹果电脑应用案例

类里面套一个类，这种写法可以禁止直接实例化一个类的简洁方式

一个苹果电脑的例子，制造商将所有的硬件规格都隐藏了起来，客户只知道去买某个品牌和型号的笔记本

可以看到只有AppleFactory类实例化, 但生产的其他参数都隐藏了起来，无法直接实例化生产过程MacMini14类
过程的参数，让购买者无需关心内部生产的过程

MINI14 = '1.4GHZ Mac mini'class AppleFactory:class MacMini14:def __init__(self):self.memory = 4 # 单位为GBself.hdd = 500 # 单位为GBself.gpu = 'Intel HD Graphics 5000'def __str__(self):info = ('Model: {}'.format(MINI14),'Memory: {}GB'.format(self.memory),'Hard Disk: {}GB'.format(self.hdd),'Graphics Card: {}'.format(self.gpu))return '\n'.join(info)def build_computer(self, model):if (model == MINI14):return self.MacMini14()else:print("I don't know how to build {}".format(model))if __name__ == '__main__':afac = AppleFactory()mac_mini = afac.build_computer(MINI14)print(mac_mini)

使用命名参数

使用实参列表展开

工厂模式和建造者模式的区别

1. 工厂模式以单个步骤创建对象，创建者模式以多个步骤创建对象，并且几乎始终会使用一个指挥者。
2. 在工厂模式下，会立即返回一个创建好的对象；而在建造者模式下，仅在需要时客户端代码才显示地请求指挥者返回最终的对象

2. 案例二：作为指挥者向制造商提供指令，制作想要的电脑

首先实例化HardwareEngineer,调用并传参construct_computer(self, memory, hdd, gpu)，再去实例化ComputerBuilder()--> Computer()

列表式执行函数

        [step for step in (self.builder.configure_momory(memory),self.builder.configure_hdd(hdd),self.builder.configure_gpu(gpu))]

class Computer:def __init__(self, serial_number):self.serial = serial_numberself.memory = None  # 单位为GBself.hdd = None     # 单位为GBself.gpu = Nonedef __str__(self):info = ('Memory: {}GB'.format(self.memory),'Hard Disk: {}GB'.format(self.hdd),'Graphics Card: {}'.format(self.gpu))return '\n'.join(info)class ComputerBuilder:def __init__(self):self.computer = Computer('AG23385193')def configure_momory(self, amount):self.computer.memory = amountdef configure_hdd(self, amount):self.computer.hdd = amountdef configure_gpu(self, gpu_model):self.computer.gpu = gpu_modelclass HardwareEngineer:def __init__(self):self.builder = Nonedef construct_computer(self, memory, hdd, gpu):self.builder = ComputerBuilder()[step for step in (self.builder.configure_momory(memory),self.builder.configure_hdd(hdd),self.builder.configure_gpu(gpu))]@propertydef computer(self):return self.builder.computerdef main():engineer = HardwareEngineer()engineer.construct_computer(hdd=500, memory=8, gpu='GeForce GTX 650 Ti')computer = engineer.computerprint(computer)if __name__ == '__main__':'''通过HardwareEngineer（传参调用ComputerBuilder,可以使用其他类也可以） --> ComputerBuilder --> Computer(负责打印输出数据)'''main()

可以看出，类实例化是一层一层的进行的，但是得指挥者main()却只是执行时进行了一次实例化

3. 使用建造者（builder）模式制作Pizza

制作披萨需要特定的顺序，才能制作:

先要准备：配料、调味料、生面团

然后，生面团上面撒上调味料和配料

根据不同的pizza的要求，有不同的烘焙时间，依赖于生面团的厚度和使用的配料

应用中有两个建造者：

1. 制作玛格丽特披萨（MargaritaBuilder）
2. 制作奶油熏肉披萨（CreamyBaconBuilder）

from enum import Enum
import timePizzaProgress = 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: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 your {}...'.format(self.dough.name, self))time.sleep(STEP_DELAY)print('done with the {} dough'.format(self.dough.name))class MargaritaBuilder: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 CreamyBaconBuilder:def __init__(self):self.pizza = Pizza('creamy bacon')self.progress = PizzaProgress.queuedself.baking_time = 7def prepare_dough(self):self.progress = PizzaProgress.preparationself.pizza.prepare_dough(PizzaDough.thick)def add_sauce(self):print('adding the creme fraiche sauce to your creamy bacon')self.pizza.sauce = PizzaSauce.creme_fraichetime.sleep(STEP_DELAY)print('done with the creme fraiche sauce')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, mushroom, red onion, oregano)')def bake(self):self.progress = PizzaProgress.bakingprint('baking your creamy bacon for {} second'.format(self.baking_time))time.sleep((self.baking_time))self.progress = PizzaProgress.readyprint('your creamy bacon is ready')class Waiter: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 validata_style(builders):try:pizza_style = input('What pizza would you like, [m]argarita or [c]reamy bacon? ')builder = builders[pizza_style]()valid_input = Trueexcept KeyError as err:print('Sorry, only margarita (key m) and creamy bacon (key c) are available')return (False, None)return (True, builder)def main():builders = dict(m=MargaritaBuilder, c=CreamyBaconBuilder)valid_input = Falsewhile not valid_input:valid_input, builder = validata_style(builders)print()waiter = Waiter()waiter.construct_pizza(builder)pizza = waiter.pizzaprint()print('Enjoy your {}!'.format(pizza))if __name__ == '__main__':main()

4.链式调用建造者方法（流利的建造者）：Pizza链式方法

Pizza类中包含PizzaBuilder()

build() 实例化Pizza(), 传入参数self,就是Pizza的形参builder

class Pizza:def __init__(self, builder):self.garlic = builder.garlicself.extra_cheese = builder.extra_cheesedef __str__(self):garlic = 'yes' if self.garlic else 'no'cheese = 'yes' if self.extra_cheese else 'no'info = ('Garlic: {}'.format(garlic), 'Extra cheese: {}'.format(cheese))return '\n'.join(info)class PizzaBuilder:def __init__(self):self.extra_cheese = Falseself.garlic = Falsedef add_garlic(self):self.garlic = Truereturn selfdef add_extra_cheese(self):self.extra_cheese = Truereturn selfdef build(self):# 实例化Pizza(), 传入参数self,就是Pizza的形参builderreturn Pizza(self)if __name__ == '__main__':# Pizza类中包含PizzaBuilder()pizza = Pizza.PizzaBuilder().add_garlic().add_extra_cheese().build()print(pizza)# a = Pizza# print(a)# b = a.PizzaBuilder()# print(b)# c = b.add_garlic().add_extra_cheese().build()# print(c)