python 观察者模式怎么写

# 主题/可观察者接口
class Subject:
    def __init__(self):
        self._observers = []  # 存储所有观察者
        
    def attach(self, observer):
        """添加观察者"""
        if observer not in self._observers:
            self._observers.append(observer)
            
    def detach(self, observer):
        """移除观察者"""
        try:
            self._observers.remove(observer)
        except ValueError:
            pass
            
    def notify(self, *args, **kwargs):
        """通知所有观察者"""
        for observer in self._observers:
            observer.update(*args, **kwargs)


# 具体主题实现
class ConcreteSubject(Subject):
    def __init__(self):
        super().__init__()
        self._state = None  # 主题的状态
        
    @property
    def state(self):
        return self._state
        
    @state.setter
    def state(self, value):
        self._state = value
        # 状态改变时通知所有观察者
        self.notify(self._state)


# 观察者接口
class Observer:
    def update(self, *args, **kwargs):
        """当主题状态改变时调用"""
        raise NotImplementedError("子类必须实现update方法")


# 具体观察者1
class ConcreteObserver1(Observer):
    def update(self, *args, **kwargs):
        print(f"观察者1接收到更新: {args[0]}")


# 具体观察者2
class ConcreteObserver2(Observer):
    def update(self, *args, **kwargs):
        print(f"观察者2接收到更新: {args[0]}")


# 使用示例
if __name__ == "__main__":
    # 创建主题
    subject = ConcreteSubject()
    
    # 创建观察者
    observer1 = ConcreteObserver1()
    observer2 = ConcreteObserver2()
    
    # 注册观察者
    subject.attach(observer1)
    subject.attach(observer2)
    
    # 改变主题状态，会自动通知观察者
    subject.state = "状态1"
    subject.state = "状态2"
    
    # 移除一个观察者
    subject.detach(observer1)
    print("\n移除观察者1后:")
    subject.state = "状态3"