observer.py

#!/usr/bin/python
#coding=utf-8
#****************************************************
# Author: XYJ - xyj.asmy@gmail.com
# Last modified: 2012-07-02 09:44
# Filename: observer.py
# Description:
#****************************************************


class Observable(object):

    _list = []
    changed = False

    def add_observer(self, obj):
        self._list.append(obj)

    def remove_observer(self, index):
        return self._list.pop(index)

    def remove_all_observers(self):
        self._list = []

    def set_changed(self):
        self.changed = True if self.changed else False
        return self.changed

    def notify_observers(self, *args, **kwargs):
        for obj in self._list:
            obj.update(*args, **kwargs)

if __name__ == '__main__':
    class Subject(Observable):

        def set_price(self, price):
            self.set_changed()
            self.notify_observers(price)

    class Observer(object):

        def __init__(self, name):
            self.name = name

        def update(self, *args, **kwargs):
            print "%s the price is %s" % (self.name, args[0])

    sub = Subject()
    sub.add_observer(Observer(1))
    sub.add_observer(Observer('a'))
    sub.set_price(10)
    sub.remove_observer(1)
    sub.set_price(20)