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GB
self.hdd = 500 # 单位为GB
self.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 '
'.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)
工厂模式和建造者模式的区别
- 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。
- 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_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 '
'.join(info)
class ComputerBuilder:
def __init__(self):
self.computer = Computer('AG23385193')
def configure_momory(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()
[step for step in (self.builder.configure_momory(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__':
'''
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：
- 制作玛格丽特披萨（MargaritaBuilder）
- 制作奶油熏肉披萨（CreamyBaconBuilder）
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
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
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
def prepare_dough(self):
self.progress = PizzaProgress.preparation
self.pizza.prepare_dough(PizzaDough.thick)
def add_sauce(self):
print('adding the creme fraiche sauce to your creamy bacon')
self.pizza.sauce = PizzaSauce.creme_fraiche
time.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.baking
print('baking your creamy bacon for {} second'.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
[step() for step in (builder.prepare_dough,
builder.add_sauce, builder.add_topping, builder.bake)]
@property
def pizza(self):
return self.builder.pizza
def validata_style(builders):
try:
pizza_style = input('What pizza would you like, [m]argarita or [c]reamy bacon? ')
builder = builders[pizza_style]()
valid_input = True
except 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 = False
while not valid_input:
valid_input, builder = validata_style(builders)
print()
waiter = Waiter()
waiter.construct_pizza(builder)
pizza = waiter.pizza
print()
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.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 '
'.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):
# 实例化Pizza(), 传入参数self,就是Pizza的形参builder
return 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)