Head First 设计模式——观察者模式(Observer Pattern)——Python实现(1)
2011-06-14 00:28
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作者:liuyuan_jq
2011-06-13
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。
气象组件实现观察者接口
布告栏显示接口
observer.py
weatherData.py
displayElement.py
测试
weatherStation.py
weatherStationHeatIndex.py
作者:liuyuan_jq
2011-06-13
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。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。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。
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")
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 Subject class 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 Observer
from weatherData import WeatherData
class 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))
测试
weatherStation.py
#!/usr/bin/env python # -*- coding:utf-8 -*- from weatherData import WeatherData from 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% humidity Avg/Max/Min temperature = 80.0/80/80 Forecast: Improving weather on the way! Current conditions: 82F degrees and 70% humidity Avg/Max/Min temperature = 81.0/82/80 Forecast: Watch out for cooler, rainy weather Current conditions: 78F degrees and 90% humidity Avg/Max/Min temperature = 80.0/82/78 Forecast: More of the same
weatherStationHeatIndex.py
#!/usr/bin/env python # -*- coding:utf-8 -*- from weatherData import WeatherData from 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% humidity Avg/Max/Min temperature = 80.0/80/80 Forecast: Improving weather on the way! Heat index is 82.9553506371 Current conditions: 82F degrees and 70% humidity Avg/Max/Min temperature = 81.0/82/80 Forecast: Watch out for cooler, rainy weather Heat index is 86.9012330639 Current conditions: 78F degrees and 90% humidity Avg/Max/Min temperature = 80.0/82/78 Forecast: More of the same Heat index is 83.6496713956
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