# 輪子,引擎, 車身這些定義好了都不需要變動
class Wheel:
  def __init__(self, name):
    self.name = name
  def accept(self, visitor):
    # 每個visitor是同樣的，但是其中的方法是不一樣的，比如這里是visitWheel，
    # 然后傳入了self，想想？他其實(shí)想做什么就能做什么
    visitor.visitWheel(self)

class Engine:
  def accept(self, visitor):
    visitor.visitEngine(self)

class Body:
  def accept(self, visitor):
    visitor.visitBody(self)

# 我們要組合成車
class Car:
  def __init__(self):
    self.engine = Engine()
    self.body  = Body()
    self.wheels = [ Wheel("front left"), Wheel("front right"),
            Wheel("back left") , Wheel("back right") ]

  # 這個也不需要在動，他只是上面部件的組合，只是做了屬性的委托
  def accept(self,visitor):
    visitor.visitCar(self)
    self.engine.accept(visitor)
    self.body.accept(visitor)
    for wheel in self.wheels:
      wheel.accept(visitor)

# 這個才是我們的訪問者，每次的修改都在這里面
class PrintVisitor:
  def visitWheel(self, wheel):
    print "Visiting "+wheel.name+" wheel"
  def visitEngine(self, engine):
    print "Visiting engine"
  def visitBody(self, body):
    print "Visiting body"
  def visitCar(self, car):
    print "Visiting car"

if __name__ == '__main__':
  car = Car()
  visitor = PrintVisitor()
  car.accept(visitor)

# 這個是觀察者基類
class Subject(object):
  def __init__(self):
    self._observers = []

  # 添加依賴的對象
  def attach(self, observer):
    if not observer in self._observers:
      self._observers.append(observer)

  # 取消添加
  def detach(self, observer):
    try:
      self._observers.remove(observer)
    except ValueError:
      pass

  # 這里只是通知上面注冊的依賴對象新的變化
  def notify(self, modifier=None):
    for observer in self._observers:
      # 可以設(shè)置過濾條件，對不符合過濾條件的更新
      if modifier != observer:
        observer.update(self)


# 觀察者類
class Data(Subject):
  def __init__(self, name=''):
    super(Data, self).__init__()
    self.name = name
    self._data = 0

  # python2.6新增的寫法,獲取屬性為property，設(shè)置屬性為(假設(shè)屬性名字為x)@x.setter,刪除為@x.deleter
  @property
  def data(self):
    return self._data

  @data.setter
  def data(self, value):
    self._data = value
    self.notify()

# 這里有2個被觀察者，也就是依賴的對象，每次Data有改變，這2個view都會變動
class HexViewer(object):
  def update(self, subject):
    print 'HexViewer: Subject %s has data 0x%x' % (subject.name, subject.data)

class DecimalViewer(object):
  def update(self, subject):
    print 'DecimalViewer: Subject %s has data %d' % (subject.name, subject.data)


if __name__ == '__main__':

  data1 = Data('Data 1')
  data2 = Data('Data 2')
  view1 = DecimalViewer()
  view2 = HexViewer()
  data1.attach(view1)
  data1.attach(view2)
  data2.attach(view2)
  data2.attach(view1)

  print "Setting Data 1 = 10"
  data1.data = 10
  print "Setting Data 2 = 15"
  data2.data = 15
  print "Setting Data 1 = 3"
  data1.data = 3
  print "Setting Data 2 = 5"
  data2.data = 5
  print "Update data1's view2 Because view1 is be filtered"
  data1.notify(modifier=view1) 
  print "Detach HexViewer from data1 and data2."
  data1.detach(view2)
  data2.detach(view2)
  print "Setting Data 1 = 10"
  data1.data = 10
  print "Setting Data 2 = 15"
  data2.data = 15