观察者模式

#!/usr/bin/python
# coding:utf8
'''
Observer
'''


class Subject(object):  # 发布者基类
    def __init__(self):
        self._observers = []
        self._modifier = []

    def attach(self, observer):  # 添加
        if not observer in self._observers:
            self._observers.append(observer)

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

    def notify(self):  # 通知
        for observer in self._observers:
            if observer not in self._modifier:
                observer.update(self)


# 发布者
class Data(Subject):
    def __init__(self, name=''):
        super(Data, self).__init__()
        self.name = name
        self._data = 0

    def defriend(self, observer):  # 拉黑
        if not observer in self._modifier:
            self._modifier.append(observer)

    def friend(self, observer):  # 取消拉黑
        try:
            self._modifier.remove(observer)
        except ValueError:
            pass

    @property
    def data(self):
        return self._data

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


# 订阅者
class HexViewer:
    def update(self, subject):
        print('HexViewer: Subject %s has data 0x%x' %  # 十六进制
              (subject.name, subject.data))


class DecimalViewer:
    def update(self, subject):
        print('DecimalViewer: Subject %s has data %d' %  # 十进制
              (subject.name, subject.data))


# Example usage...
def main():
    data1 = Data('Data 1')
    data2 = Data('Data 2')
    view1 = DecimalViewer()
    view2 = HexViewer()
    data1.attach(view1)
    data1.defriend(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("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


if __name__ == '__main__':
    main()