# 这个是观察者基类
class Subject(object):def __init__(self):self._observers = []# 添加依赖的对象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# 这里只是通知上面注册的依赖对象新的变化def notify(self, modifier=None):for observer in self._observers:# 可以设置过滤条件，对不符合过滤条件的更新if modifier != observer:observer.update(self)# 观察者类
class Data(Subject):def __init__(self, name=''):super(Data, self).__init__()self.name = nameself._data = 0# python2.6新增的写法,获取属性为property，设置属性为(假设属性名字为x)@x.setter,删除为@x.deleter
    @propertydef data(self):return self._data@data.setterdef data(self, value):self._data = valueself.notify()# 这里有2个被观察者，也就是依赖的对象，每次Data有改变，这2个view都会变动
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 = 10print "Setting Data 2 = 15"data2.data = 15print "Setting Data 1 = 3"data1.data = 3print "Setting Data 2 = 5"data2.data = 5print "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 = 10print "Setting Data 2 = 15"data2.data = 15