Python设计模式构建者模式

构建者模式是一种独特的设计模式，它有助于使用简单的对象来构建复杂的对象，并使用一种算法方法。这种设计模式属于创造模式的范畴。在这种设计模式中，一个构建器类以逐步的程序构建最终的对象。这个构建器是独立于其他对象的。

构建者模式的优点

它在类所创建的特定对象的构建和表示之间提供了清晰的分离和独特的层次。
它提供了对所创建模式的构建过程的更好控制。
它提供了一个完美的方案来改变对象的内部表示。

如何实现构建者模式

在本节中，我们将学习如何实现构建者模式。

class Director:
   __builder = None

   def setBuilder(self, builder):
      self.__builder = builder

   def getCar(self):
      car = Car()

      # First goes the body
      body = self.__builder.getBody()
      car.setBody(body)

      # Then engine
      engine = self.__builder.getEngine()
      car.setEngine(engine)

      # And four wheels
      i = 0
      while i < 4:
         wheel = self.__builder.getWheel()
            car.attachWheel(wheel)
         i += 1
      return car

# The whole product
class Car:
   def __init__(self):
      self.__wheels = list()
      self.__engine = None
      self.__body = None

   def setBody(self, body):
      self.__body = body

   def attachWheel(self, wheel):
      self.__wheels.append(wheel)

   def setEngine(self, engine):
      self.__engine = engine

   def specification(self):
      print "body: %s" % self.__body.shape
      print "engine horsepower: %d" % self.__engine.horsepower
      print "tire size: %d\'" % self.__wheels[0].size

class Builder:
      def getWheel(self): pass
      def getEngine(self): pass
      def getBody(self): pass

class JeepBuilder(Builder):

   def getWheel(self):
      wheel = Wheel()
      wheel.size = 22
      return wheel

   def getEngine(self):
      engine = Engine()
      engine.horsepower = 400
      return engine

   def getBody(self):
      body = Body()
      body.shape = "SUV"
      return body

# Car parts
class Wheel:
   size = None

class Engine:
   horsepower = None

class Body:
   shape = None

def main():
   jeepBuilder = JeepBuilder() # initializing the class

   director = Director()

   # Build Jeep
   print "Jeep"
   director.setBuilder(jeepBuilder)
   jeep = director.getCar()
   jeep.specification()
   print ""

if __name__ == "__main__":
   main()