23种设计模式介绍（Python示例讲解）(34)

以下是观察者模式的 Python 实现：
class Subject: def __init__(self): self._observers = [] def attach(self, observer): if observer not in self._observers: self._observers.append(observer) def detach(self, observer): try: self._observers.remove(observer) except ValueError: pass def notify(self, modifier=None): for observer in self._observers: if modifier != observer: observer.update(self)class Observer: def update(self, subject): passclass ConcreteSubject(Subject): def __init__(self): super().__init__() self._state = None @property def state(self): return self._state @state.setter def state(self, state): self._state = state self.notify()class ConcreteObserver(Observer): def __init__(self, name): self._name = name def update(self, subject): print(f"{self._name} received an update: {subject.state}")subject = ConcreteSubject()observer1 = ConcreteObserver("Observer 1")observer2 = ConcreteObserver("Observer 2")subject.attach(observer1)subject.attach(observer2)subject.state = 123subject.detach(observer1)subject.state = 456