Python笔记之观察者模式

from abc import ABCMeta, abstractmethodclass Publisher:  """被观察者：发布/订阅关系中的发布对象"""  def __init__(self):    self.subscribers = []    self.latest_content = None  def set_content(self, content):    """有新消息时，发布新的消息"""    self.latest_content = content    self.publish()  def get_latest_content(self):    """获取最新的消息"""    return self.latest_content  def register(self, subscriber):    """注册一个新的订阅者"""    self.subscribers.append(subscriber)  def publish(self):    """发布消息并通知订阅的用户"""    for subscriber in self.subscribers:      subscriber.notify()class Subscriber(metaclass=ABCMeta):  """观察者的抽象类：需要定义一个通知接口，用于发布对象通知订阅的用户"""  @abstractmethod  def notify(self):    passclass SubscriberA(Subscriber):  """观察者A：发布/订阅关系中的订阅者，当订阅的发布者有新的变化或动态的时候能及时收到通知"""  def __init__(self):    self.my_publisher = None  def subscribe(self, publisher):    """订阅并进行注册"""    self.my_publisher = publisher    self.my_publisher.register(self)  def notify(self):    """获取最新消息"""    latest_content = self.my_publisher.get_latest_content()    print(self, latest_content)class SubscriberB(Subscriber):  """观察者B：发布/订阅关系中的订阅者，当订阅的发布者有新的变化或动态的时候能及时收到通知"""  def __init__(self):    self.my_publisher = None  def subscribe(self, publisher):    """订阅并进行注册"""    self.my_publisher = publisher    self.my_publisher.register(self)  def notify(self):    """获取最新消息"""    latest_content = self.my_publisher.get_latest_content()    print(self, latest_content)if __name__ == '__main__':  new_publisher = Publisher()  subscriber_a = SubscriberA()  subscriber_a.subscribe(new_publisher)  subscriber_b = SubscriberB()  subscriber_b.subscribe(new_publisher)  new_publisher.set_content('This is a new message!')