建造者模式
可以用于细粒度控制复杂对象的创建过程
想象一下，我们想要创建一个由多个部分构成的对象，而且它的构成需要一部接一部地完成。
只有当各个部分都创建好，这个对象才算是完整的。
建造者模式：讲一个复杂对象的构造过程与其表现分离，这样，同一个构造过程可用于创建多个不同的表现和网页。
eg:HTML页面生成问题
参与者：
建造者：负责创建复杂对象的各个组成部分
指挥者：
建造者模式与工厂模式的区别：
工厂模式以单个步骤创建对象；建造者模式以多个步骤创建对象。
工厂模式会立即返回一个创建好的对象；建造者模式仅在需要时客户端代码才显式地请求指挥者返回最终的对象。
建造者模式：
如果我们知道一个对象必须经过多个步骤来创建，并且要求同一个构造过程可以产生不同的表现，就可以使用建造者模式。
- 要创建一个复杂对象（该对象由多个部分构成，切对象的创建要经过多个不同的步骤，这些步骤也许还需要遵从特定的顺序）
- 要求一个对象能有不同的表现，并希望将对象的构造与表现解耦
- 想要在某个时间点创建对象，但在稍后的时间点在访问
# coding: utf-8 class Computer: def __init__(self, serial_number): self.serial = serial_number self.memory = None # 单位为GB self.hdd = None # 单位为GB self.gpu = None def __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_memory(self, amount): self.computer.memory = amount def configure_hdd(self, amount): self.computer.hdd = amount def configure_gpu(self, gpu_model): self.computer.gpu = gpu_model class HardwareEngineer: def __init__(self): self.builder = None def construct_computer(self, memory, hdd, gpu): self.builder = ComputerBuilder() self.builder.configure_memory(memory) self.builder.configure_hdd(hdd) self.builder.configure_gpu(gpu) @property def computer(self): return self.builder.computer def main(): engineer = HardwareEngineer() engineer.construct_computer(hdd=500, memory=8, gpu='GeForce GTX 650 Ti') computer = engineer.computer print(computer) if __name__ == '__main__': main()
例2：
# coding: utf-8 from enum import Enum import time PizzaProgress = 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 = 3 # 考虑是示例，单位为秒 class Pizza: def __init__(self, name): self.name = name self.dough = None self.sauce = None self.topping = [] def __str__(self): return self.name def prepare_dough(self, dough): self.dough = dough print('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.queued self.baking_time = 5 # 考虑是示例，单位为秒 def prepare_dough(self): self.progress = PizzaProgress.preparation self.pizza.prepare_dough(PizzaDough.thin) def add_sauce(self): print('adding the tomato sauce to your margarita...') self.pizza.sauce = PizzaSauce.tomato time.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.baking print('baking your margarita for {} seconds'.format(self.baking_time)) time.sleep(self.baking_time) self.progress = PizzaProgress.ready print('your margarita is ready') class CreamyBaconBuilder: def __init__(self): self.pizza = Pizza('creamy bacon') self.progress = PizzaProgress.queued self.baking_time = 7 # 考虑是示例，单位为秒 def prepare_dough(self): self.progress = PizzaProgress.preparation self.pizza.prepare_dough(PizzaDough.thick) def add_sauce(self): print('adding the crème fraîche sauce to your creamy bacon') self.pizza.sauce = PizzaSauce.creme_fraiche time.sleep(STEP_DELAY) print('done with the crème fraîche 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, mushrooms, red onion, oregano)') def bake(self): self.progress = PizzaProgress.baking print('baking your creamy bacon for {} seconds'.format(self.baking_time)) time.sleep(self.baking_time) self.progress = PizzaProgress.ready print('your creamy bacon is ready') class Waiter: def __init__(self): self.builder = None def construct_pizza(self, builder): self.builder = builder self.builder.prepare_dough() self.builder.add_sauce() self.builder.add_topping() self.builder.bake() @property def pizza(self): return self.builder.pizza def validate_style(builders): try: pizza_style = input('What pizza would you like, [m]argarita or [c]reamy bacon? ') builder = builders[pizza_style]() except KeyError: 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 = False while not valid_input: valid_input, builder = validate_style(builders) print() waiter = Waiter() waiter.construct_pizza(builder) pizza = waiter.pizza print() print('Enjoy your {}!'.format(pizza)) if __name__ == '__main__': main()
有趣的建造这模式变体，
会链式的调用建造者方法，通过将建造者本身定义为内部类并从其每个设置器方法返回自身来实现。
build方法返回最终对象。
# coding: utf-8 class Pizza: def __init__(self, builder): self.garlic = builder.garlic self.extra_cheese = builder.extra_cheese def __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 = False self.garlic = False def add_garlic(self): self.garlic = True return self def add_extra_cheese(self): self.extra_cheese = True return self def build(self): return Pizza(self) if __name__ == '__main__': pizza = Pizza.PizzaBuilder().add_garlic().add_extra_cheese().build() print(pizza)
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