代码

# -.- coding:utf-8 -.-
# __author__ == 'zhengtong'
from __future__ import print_function


def exception_wrapper(func):
    def wrapper(self, *args, **kwargs):
        try:
            result = func(self, *args, **kwargs)
            if result is not None:
                return result
        except Exception:
            import sys, traceback
            ex_type, ex, tb = sys.exc_info()
            traceback.print_exception(ex_type, ex, tb)
            return False
        return True
    return wrapper


class Producer(object):

    def __init__(self):
        self.topic = {}

    @exception_wrapper
    def create_topic(self, topic):
        if topic not in self.topic:
            self.topic[topic] = []

    @exception_wrapper
    def publish(self, topic, data):
        self.create_topic(topic)
        if not self.topic[topic]:
            return '当前主题没有任何观察者/订阅者/消费者'
        self.notify_observers(topic, data)

    @exception_wrapper
    def subscribe(self, topic, *observers):
        self.create_topic(topic)
        for observer in observers:
            if observer not in self.topic[topic]:
                self.topic[topic].append(observer)

    @exception_wrapper
    def unsubscribe(self, topic, *observers):
        l = self.topic[topic]
        for observer in observers:
            l.pop(l.index(observer))

    @exception_wrapper
    def notify_observers(self, topic, data):
        for observer in self.topic[topic]:
            observer.get_message(data)


class SendMailObserver(object):

    def get_message(self, data):
        print('send mail to: ', data)


class WriteMailObserver(object):

    def get_message(self, data):
        print('write mail to: ', data)


class ProcessMailObserver(object):

    def get_message(self, data):
        print('ProcessMail mail: ', data)

if __name__ == '__main__':
    # 启动Producer服务
    producer = Producer()

    # 创建主题
    producer.create_topic('sss')
    producer.create_topic('bbb')

    # 注册观察者/订阅者/消费者
    send_mail_observer = SendMailObserver()
    write_mail_observer = WriteMailObserver()
    Process_mail_observer = ProcessMailObserver()
    producer.subscribe('send_mail', *[send_mail_observer,
                                      write_mail_observer,
                                      Process_mail_observer])

    # 查看每个队列有多少的consumer
    print('producer.topic: ', producer.topic)

    # 发布消息
    producer.publish('send_mail', '330356463@qq.com')

    # 移除观察者/订阅者/消费者
    producer.unsubscribe('send_mail', write_mail_observer)

    # 查看每个队列有多少的consumer
    print(producer.topic)

    # 查看现在总共有几个频道
    print(producer.topic.keys())


# 显示结果
producer.topic:  {'bbb': [], 'sss': [], 'send_mail': [<__main__.SendMailObserver object at 0x03492F50>, <__main__.WriteMailObserver object at 0x03492F70>, <__main__.ProcessMailObserver object at 0x03492F90>]}
send mail to:  330356463@qq.com
write mail to:  330356463@qq.com
ProcessMail mail:  330356463@qq.com
{'bbb': [], 'sss': [], 'send_mail': [<__main__.SendMailObserver object at 0x03492F50>, <__main__.ProcessMailObserver object at 0x03492F90>]}
['bbb', 'sss', 'send_mail']

模式总结

观察者模式强调的是松耦合，通过程序之间的强约定弱依赖实现通用场景的<发布/订阅>模型。

核心理念

当数据发生变化时执行回调函数(provide a callback for notification of events/changes to data).

模式类型

行为模式

设计原则

1. 为了交互对象之间的松耦合设计而努力。

参考

• [x] Head First设计模式
• [x] Head First设计模式Python版源码
• [x] patterns-idioms
• [x] py-patterns