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Introduction
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Null 模式
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<a href="." >Builder 模式</a>
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<h1 id="python设计模式之builder模式"><a href="http://dongweiming.github.io/python-builder.html"Permalink to python设计模式之Builder模式"" target="_blank">python设计模式之Builder模式</a></h1><h2 id="builder模式">Builder模式</h2><p>Builder模式帮你把一个不同类的大工程分开成不同的部分，最后在把这些合并起来</p><h2 id="python的例子">python的例子</h2><p>制造一辆车的工序是很繁琐和浩大的，我们可以定一个车辆的描述</p><pre><code>class Vehicle(object):
def __init__(self, type_name):
self.type = type_name
self.wheels = None
self.doors = None
self.seats = None
# 不同的车子类型，齿轮，车门数，座位数都不尽相同
def view(self):
print(
"This vehicle is a " +
self.type +
" with; " +
str(self.wheels) +
" wheels, " +
str(self.doors) +
" doors, and " +
str(self.seats) +
" seats."
)</code></pre>
<p>这里我要把制造齿轮，车门，座位的工序抽象出来，用不同的制造部门去做</p><pre><code>class VehicleBuilder(object):
__metadata__ = abc.ABCMeta
# 装饰器定义抽象方法（只能用在 metaclass 为 abc.ABCMeta 或其子类的 class 中）
# 这里其实当然可以用pass，或者raise一个基类未实现的异常
@abc.abstractmethod
def make_wheels(self):
raise
@abc.abstractmethod
def make_doors(self):
raise
@abc.abstractmethod
def make_seats(self):
raise</code></pre>
<p>然后设想我要制造汽车和自行车， 每个都要继承这个VehicleBuilder基类，但是齿轮，车门，座位都是不一样的</p><pre><code>class CarBuilder(VehicleBuilder):
def __init__(self):
self.vehicle = Vehicle("Car ")
def make_wheels(self):
self.vehicle.wheels = 4
def make_doors(self):
self.vehicle.doors = 3
def make_seats(self):
self.vehicle.seats = 5
class BikeBuilder(VehicleBuilder):
def __init__(self):
self.vehicle = Vehicle("Bike")
def make_wheels(self):
self.vehicle.wheels = 2
def make_doors(self):
self.vehicle.doors = 0
def make_seats(self):
self.vehicle.seats = 2</code></pre>
<p>下面是最重要的环节：制造的Director</p><pre><code>class VehicleManufacturer(object):
def __init__(self):
self.builder = None
# 根据传进来的builder制造它提供的产品规格
def create(self):
assert not self.builder is None, "No defined builder"
self.builder.make_wheels()
self.builder.make_doors()
self.builder.make_seats()
return self.builder.vehicle</code></pre>
<p>看起来是不是有点和以前的模式不好分辨？ 主要下面的调用方式</p><pre><code>if __name__ == "__main__":
manufacturer = VehicleManufacturer()
# 重要的是这样的调用方式，每次修改builder方法传入不同的要求，然后在create里面去制造，
# 整个过程都是在VehicleManufacturer完成
manufacturer.builder = CarBuilder()
car = manufacturer.create()
car.view()
manufacturer.builder = BikeBuilder()
bike = manufacturer.create()
bike.view()</code></pre>
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