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先看代码：

# 导入未来模块以支持类型注解
from __future__ import annotations# 导入抽象基类模块和随机数生成器
from abc import ABC, abstractmethod
from random import randrange# 导入列表类型注解
from typing import List# 定义观察者模式中的主体接口（Subject）
class Subject(ABC):"""主体接口声明一组用于管理订阅者的方法。"""@abstractmethoddef attach(self, observer: Observer) -> None:"""将观察者附加到主体。"""pass@abstractmethoddef detach(self, observer: Observer) -> None:"""从主体中移除观察者。"""pass@abstractmethoddef notify(self) -> None:"""通知所有观察者有关事件的信息。"""pass# 定义具体主体类（ConcreteSubject）
class ConcreteSubject(Subject):"""具体主体拥有对所有订阅者至关重要的状态，并在状态变化时通知观察者。"""_state: int = None"""为了简化起见，主体的状态（对所有订阅者至关重要）存储在此变量中。"""_observers: List[Observer] = []"""订阅者列表。在实际应用中，订阅者列表可以更全面地存储（按事件类型分类等）。"""def attach(self, observer: Observer) -> None:print("主体：已附加一个观察者。")self._observers.append(observer)def detach(self, observer: Observer) -> None:self._observers.remove(observer)"""订阅管理方法。"""def notify(self) -> None:"""触发每个订阅者的更新。"""print("主体：正在通知观察者...")for observer in self._observers:observer.update(self)def some_business_logic(self) -> None:"""通常，订阅逻辑只是主体所能做的工作的一部分。主体通常包含一些重要的业务逻辑，当即将发生（或已经发生）重要事情时触发通知方法。"""print("\n主体：我正在做一些重要的事情。")self._state = randrange(0, 10)print(f"主体：我的状态刚刚变更为：{self._state}")self.notify()# 定义观察者接口（Observer）
class Observer(ABC):"""观察者接口声明由主体使用的update方法。"""@abstractmethoddef update(self, subject: Subject) -> None:"""接收主体的更新。"""pass# 定义具体观察者类（ConcreteObserverA 和 ConcreteObserverB）
"""
具体观察者对它们所附属的主体发出的更新做出反应。
"""class ConcreteObserverA(Observer):def update(self, subject: Subject) -> None:if subject._state < 3:print("具体观察者A：对事件作出反应")class ConcreteObserverB(Observer):def update(self, subject: Subject) -> None:if subject._state == 0 or subject._state >= 2:print("具体观察者B：对事件作出反应")# 客户端代码
if __name__ == "__main__":subject = ConcreteSubject()observer_a = ConcreteObserverA()subject.attach(observer_a)observer_b = ConcreteObserverB()subject.attach(observer_b)subject.some_business_logic()subject.some_business_logic()subject.detach(observer_a)subject.some_business_logic()

输出

Subject: Attached an observer.
Subject: Attached an observer.Subject: I'm doing something important.
Subject: My state has just changed to: 0
Subject: Notifying observers...
ConcreteObserverA: Reacted to the event
ConcreteObserverB: Reacted to the eventSubject: I'm doing something important.
Subject: My state has just changed to: 5
Subject: Notifying observers...
ConcreteObserverB: Reacted to the eventSubject: I'm doing something important.
Subject: My state has just changed to: 0
Subject: Notifying observers...
ConcreteObserverB: Reacted to the event

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参考