什么是观察者模式？观察者的实现

# 抽象主题 (Subject)
class Subject:
    def __init__(self):
        self._observers = [] # 存储观察者的列表

    def attach(self, observer):
        """添加一个观察者"""
        if observer not in self._observers:
            self._observers.append(observer)
            print(f"Observer {observer.__class__.__name__} attached.")

    def detach(self, observer):
        """移除一个观察者"""
        try:
            self._observers.remove(observer)
            print(f"Observer {observer.__class__.__name__} detached.")
        except ValueError:
            print(f"Observer {observer.__class__.__name__} not found.")

    def notify(self, message):
        """通知所有观察者"""
        print("\nNotifying observers...")
        for observer in self._observers:
            observer.update(message)

# 抽象观察者 (Observer)
class Observer:
    def update(self, message):
        """接收主题通知并更新"""
        raise NotImplementedError("Subclasses must implement update method")

# 具体主题 (ConcreteSubject)
class WeatherStation(Subject):
    def __init__(self, location):
        super().__init__()
        self._location = location
        self._temperature = None
        print(f"Weather Station at {self._location} created.")

    def set_temperature(self, temp):
        """设置温度，并通知观察者"""
        if self._temperature != temp: # 只有温度变化才通知
            print(f"\n--- Weather Station at {self._location}: Temperature changing from {self._temperature} to {temp}°C ---")
            self._temperature = temp
            self.notify(f"New temperature in {self._location}: {self._temperature}°C")
        else:
            print(f"\nWeather Station at {self._location}: Temperature is still {temp}°C, no change.")

    def get_temperature(self):
        return self._temperature

# 具体观察者 (ConcreteObserver)
class PhoneDisplay(Observer):
    def __init__(self, name):
        self._name = name
        print(f"Phone Display '{self._name}' created.")

    def update(self, message):
        print(f"[{self._name} Phone Display]: Received update - {message}")

class WebDashboard(Observer):
    def __init__(self, name):
        self._name = name
        print(f"Web Dashboard '{self._name}' created.")

    def update(self, message):
        print(f"[{self._name} Web Dashboard]: Displaying - {message}")

# 实际使用
if __name__ == "__main__":
    station = WeatherStation("New York")

    phone1 = PhoneDisplay("My iPhone")
    dashboard = WebDashboard("Admin Panel")
    phone2 = PhoneDisplay("Family Tablet")

    # 注册观察者
    station.attach(phone1)
    station.attach(dashboard)
    station.attach(phone2)

    # 温度变化，通知所有观察者
    station.set_temperature(25)
    station.set_temperature(25) # 再次设置相同温度，不应通知

    # 移除一个观察者
    station.detach(phone1)

    # 再次变化，看看谁还会收到通知
    station.set_temperature(28)

    # 尝试移除一个不存在的观察者
    station.detach(PhoneDisplay("Non Existent"))

message

_observers