Head First 设计模式——观察者模式（Observer Pattern）——Python实现（1）

 

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作者：liuyuan_jq

2011-06-13

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观察者模式定义

定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有依赖都会收到通知并自动更新。观察者模式提供了一种对象设计，让主题和观察者之间松耦合。

 

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设计原则

 

 

为了交互对象之间的松耦合设计而努力。松耦合的设计之所以能让我们建立有弹性的系统，能够应对变化，是因为对象之间的互相依赖降到了最低。

 

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问题

 

 

建立下一代Internet气象观察站，该气象站必须建立在我们专利申请中的WeatherData对象上，由WeatherData对象负责追踪目前的天气状况（温度，湿度，气压）。

• 建立一个应用，有三种布告板，分别显示目前的状态、气象统计及简单的预报。
• 当WeatherObject对象获得最新的测量数据时，三种布告板必须实时更新。
• 公布一组API，让其他开发人员可以写出自己的气象布告板。

 

 

 

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设计气象站

WeatherData实现Subject接口

class Subject(object): """ 主题接口类 """ def registerObserver(observer): raise NotImplementedError("abstract Subject") def removeObserver(observer): raise NotImplementedError("abstract Subject") def notifyObservers(self): raise NotImplementedError("abstract Subject")

 

气象组件实现观察者接口

class Observer(object): """ 观察者接口类 """ def update(temp, humidity, pressure): raise NotImplementedError("abstract Observer") 

布告栏显示接口

class DisplayElement(object): def display(self): raise NotImplementedError("abstract DisplayElement") 

 

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源代码具体实现

subject.py

#!/usr/bin/env python# -*- coding:utf-8 -*-class Subject(object): """ 主题接口类 """ def registerObserver(observer): raise NotImplementedError("abstract Subject") def removeObserver(observer): raise NotImplementedError("abstract Subject") def notifyObservers(self): raise NotImplementedError("abstract Subject") 

observer.py

#!/usr/bin/env python# -*- coding:utf-8 -*-class Observer(object): """ 观察者接口类 """ def update(temp, humidity, pressure): raise NotImplementedError("abstract Observer") 

weatherData.py

#!/usr/bin/env python# -*- coding:utf-8 -*-from subject import Subjectclass WeatherData(Subject): """ 天气数据类，是一个主题类 """ # 类静态成员 observers = [] def __init__(self): self.temperature = 0.0 self.humidity = 0.0 self.pressure = 0.0 def registerObserver(self, observer): """ 注册观察者对象 """ self.observers.append(observer) def removeObserver(self, observer): """ 注销观察者对象 """ self.observers.remove(observer) def notifyObservers(self): """ 通知所有的观察者对象 """ for observer in self.observers: observer.update(self.temperature, self.humidity, self.pressure) def measurementsChanged(self): self.notifyObservers() def setMeasurements(self, temperature, humidity, pressure): self.temperature = temperature self.humidity = humidity self.pressure = pressure self.measurementsChanged() def getTemperature(self): return self.temperature def getHumidity(self): return self.humidity def getPressure(self): return self.pressure 

displayElement.py

#!/usr/bin/env python# -*- coding:utf-8 -*-from observer import Observerfrom weatherData import WeatherDataclass DisplayElement(object): def display(self): raise NotImplementedError("abstract DisplayElement")class CurrentConditionsDisplay(Observer, DisplayElement): """ 目前状况布告板 """ def __init__(self, weatherData): self.weatherData = weatherData self.weatherData.registerObserver(self) def update(self, temperature, humidity, pressure): self.temperature = temperature self.humidity = humidity self.display() def display(self): print("Current conditions: " + str(self.temperature) + "F degrees and " + str(self.humidity) + "% humidity")class ForecastDisplay(Observer, DisplayElement): """ 天气预报布告板 """ def __init__(self, weatherData): self.weatherData = weatherData self.currentPressure = 29.92 self.weatherData.registerObserver(self) def update(self, temp, humidity, pressure): self.lastPressure = self.currentPressure self.currentPressure = pressure self.display() def display(self): print("Forecast: "); if self.currentPressure > self.lastPressure: print("Improving weather on the way!") elif self.currentPressure == self.lastPressure: print("More of the same") elif self.currentPressure < self.lastPressure: print("Watch out for cooler, rainy weather")class StatisticsDisplay(Observer, DisplayElement): """ 气象统计布告板 """ def __init__(self, weatherData): self.maxTemp = 0.0 self.minTemp = 200 self.tempSum = 0.0 self.numReadings = 0 self.weatherData = weatherData self.weatherData.registerObserver(self) def update(self, temp, humidity, pressure): self.tempSum += temp self.numReadings += 1 if temp > self.maxTemp: self.maxTemp = temp if temp < self.minTemp: self.minTemp = temp self.display() def display(self): print("Avg/Max/Min temperature = " + str(self.tempSum / self.numReadings) + "/" + str(self.maxTemp) + "/" + str(self.minTemp))class HeatIndexDisplay(Observer, DisplayElement): """ 酷热指数布告板 """ def __init__(self, weatherData): self.weatherData = weatherData self.weatherData.registerObserver(self) self.heatIndex = 0.0 def update(self, t, rh, pressure): self.heatIndex = self._computeHeatIndex(t, rh) self.display() def _computeHeatIndex(self, t, rh): index = ((16.923 + (0.185212 * t) + (5.37941 * rh) - (0.100254 * t * rh) + (0.00941695 * (t * t)) + (0.00728898 * (rh * rh)) + (0.000345372 * (t * t * rh)) - (0.000814971 * (t * rh * rh)) + (0.0000102102 * (t * t * rh * rh)) - (0.000038646 * (t * t * t)) + (0.0000291583 * (rh * rh * rh)) + (0.00000142721 * (t * t * t * rh)) + (0.000000197483 * (t * rh * rh * rh)) - (0.0000000218429 * (t * t * t * rh * rh)) + 0.000000000843296 * (t * t * rh * rh * rh)) - (0.0000000000481975 * (t * t * t * rh * rh * rh))) return float(index) def display(self): print("Heat index is " + str(self.heatIndex)) 

 

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测试

 

weatherStation.py

#!/usr/bin/env python# -*- coding:utf-8 -*-from weatherData import WeatherDatafrom displayElement import *weatherData = WeatherData()currentDisplay = CurrentConditionsDisplay(weatherData)statisticsDisplay = StatisticsDisplay(weatherData)forecastDisplay = ForecastDisplay(weatherData)weatherData.setMeasurements(80, 65, 30.4)weatherData.setMeasurements(82, 70, 29.2)weatherData.setMeasurements(78, 90, 29.2) 

Current conditions: 80F degrees and 65% humidityAvg/Max/Min temperature = 80.0/80/80Forecast: Improving weather on the way!Current conditions: 82F degrees and 70% humidityAvg/Max/Min temperature = 81.0/82/80Forecast: Watch out for cooler, rainy weatherCurrent conditions: 78F degrees and 90% humidityAvg/Max/Min temperature = 80.0/82/78Forecast: More of the same 

weatherStationHeatIndex.py

#!/usr/bin/env python# -*- coding:utf-8 -*-from weatherData import WeatherDatafrom displayElement import *weatherData = WeatherData()currentDisplay = CurrentConditionsDisplay(weatherData)statisticsDisplay = StatisticsDisplay(weatherData)forecastDisplay = ForecastDisplay(weatherData)heatIndexDisplay = HeatIndexDisplay(weatherData)weatherData.setMeasurements(80, 65, 30.4)weatherData.setMeasurements(82, 70, 29.2)weatherData.setMeasurements(78, 90, 29.2) 

Current conditions: 80F degrees and 65% humidityAvg/Max/Min temperature = 80.0/80/80Forecast: Improving weather on the way!Heat index is 82.9553506371Current conditions: 82F degrees and 70% humidityAvg/Max/Min temperature = 81.0/82/80Forecast: Watch out for cooler, rainy weatherHeat index is 86.9012330639Current conditions: 78F degrees and 90% humidityAvg/Max/Min temperature = 80.0/82/78Forecast: More of the sameHeat index is 83.6496713956