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[디자인패턴] 옵저버 패턴 with python


Head First Design Pattern 에 소개되는 예제를 파이썬으로 구현하였습니다.

옵저버 패턴(Observer Pattern)

책에서는 옵저버 패턴을 아래와 같이 설명하고 있다.

한 객체의 상태가 바뀌면 그 객체에 의존하는 다른 객체들한테 연락이 가고 자동으로 내용이 갱신되는 방식으로, 일대다 의존성을 정의한다.

예제 UML

예제 구현

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class Subject(metaclass=ABCMeta):
    def registObserver(self, obj):
        pass
    
    def removeObserver(self, obj):
        pass
    
    def notifyObservers(self):
        pass

class Observer(metaclass=ABCMeta):
    def update(self):
        pass
    
class DisplayElement(metaclass=ABCMeta):
    def display(self):
        pass
    

class WeatherData(Subject):
    
    def __init__(self):
        self.observers = []
        
    def registObserver(self, obj):
        self.observers.append(obj)
        
    def removeObserver(self, obj):
        idx = self.observers.index(obj)
        del self.observers[idx]
    
    def notifyObserver(self):
        for observer in self.observers:
            observer.update(self.temperature, self.humidity, self.pressure)
    
    def measurementChanged(self):
        self.notifyObserver()
        
    def setMeasurements(self, temperature, humidity, pressure):
        self.temperature = temperature
        self.humidity = humidity
        self.pressure = pressure
        self.measurementChanged()
        

#display
class CurrentConditionsDisplay(Observer, DisplayElement):
    
    def __init__(self, weatherData):
        self.weatherData = weatherData
        self.weatherData.registObserver(self)
        
    def update(self, temperature, humidity, pressure):
        self.temperature = temperature
        self.humidity = humidity
        self.display()
        
    def display(self):
        print(f"Current Conditions: {self.temperature},{self.humidity}")

테스트

객체(WeatherData) 상태 변경하기

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weather_data = WeatherData()

current_disaply = CurrentConditionsDisplay(weather_data)
weather_data.setMeasurements(80,65,34)
weather_data.setMeasurements(85,60,34)

#Current Conditions: 80,65
#Current Conditions: 85,60

옵저버 추가하기

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class ForecastDisplay(Observer, DisplayElement):
    
    def __init__(self, weatherData):
        self.weatherData = weatherData
        self.weatherData.registObserver(self)
        
    def update(self, temperature, humidity, pressure):
        self.temperature = temperature
        self.humidity = humidity
        self.pressure = pressure
        self.display()
        
    def display(self):
        print(f"Forecast tomorrow Conditions: {self.temperature+100} - {self.humidity+100} - {self.pressure+100}")
        
forecast_disaply = ForecastDisplay(weather_data)
weather_data.setMeasurements(80,65,34)
weather_data.setMeasurements(85,60,34)

#Current Conditions: 80,65
#Forecast tomorrow Conditions: 180 - 165 - 134
#Current Conditions: 85,60
#Forecast tomorrow Conditions: 185 - 160 - 134

옵저버 삭제하기

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weather_data.removeObserver(forecast_disaply)
weather_data.setMeasurements(100,50,10)

#Current Conditions: 100,50
#

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