Python: Observer Pattern

 

GeovinDuObserver.py

# 观察者模式  Observer Pattern
# The Observer class that recieves updates from the ticker on a specific symbol:
class TickerObserver(object):

    def __init__(self, tickerSymbol):
        self.tickerSymbol = tickerSymbol
        self.lastPrice = 0.0

    def Update(self, symbol, price):
        if symbol == self.tickerSymbol:
            self.lastPrice = price

    def GetTicker(self):
        return self.tickerSymbol + " : " + str(self.lastPrice)


# The ticker subject that sends out updates to all observers:
class StockTicker(object):

    def __init__(self):
        self.observers = []

    def AttachObserver(self, tickerObserver):
        self.observers.append(tickerObserver)

    def RemoveObserver(self, tickerObserver):
        self.observers.remove(tickerObserver)

    def Notify(self, symbol, price):
        for observer in self.observers:
            observer.Update(symbol, price)


class Subject:
    """Represents what is being observed"""

    def __init__(self):

        """create an empty observer list"""

        self._observers = []

    def notify(self, modifier=None):

        """Alert the observers"""

        for observer in self._observers:
            if modifier != observer:
                observer.update(self)

    def attach(self, observer):

        """If the observer is not in the list,
        append it into the list"""

        if observer not in self._observers:
            self._observers.append(observer)

    def detach(self, observer):

        """Remove the observer from the observer list"""

        try:
            self._observers.remove(observer)
        except ValueError:
            pass


class Data(Subject):
    """monitor the object"""

    def __init__(self, name=''):
        Subject.__init__(self)
        self.name = name
        self._data = 0

    @property
    def data(self):
        return self._data

    @data.setter
    def data(self, value):
        self._data = value
        self.notify()


class HexViewer:
    """updates the Hexviewer"""

    def update(self, subject):
        print('HexViewer十六进制查看器: 实验对象 {} 转换的数据为： 0x{:x}'.format(subject.name, subject.data))


class OctalViewer:
    """updates the Octal viewer"""

    def update(self, subject):
        print('OctalViewer八进制查看器: 实验对象' + str(subject.name) + '转换的数据为 ' + str(oct(subject.data)))


class DecimalViewer:
    """updates the Decimal viewer"""

    def update(self, subject):
        print('DecimalViewer十进制查看器: 实验对象 % s 转换的数据为 % d' % (subject.name, subject.data))


"""main function"""

　　

main.py 调用：

# 观察者模式  Observer Pattern
obj1 = GeovinDuObserver.Data('Data 1')
obj2 = GeovinDuObserver.Data('Data 2')

view1 = GeovinDuObserver.DecimalViewer()
view2 = GeovinDuObserver.HexViewer()
view3 = GeovinDuObserver.OctalViewer()

obj1.attach(view1)
obj1.attach(view2)
obj1.attach(view3)

obj2.attach(view1)
obj2.attach(view2)
obj2.attach(view3)

obj1.data = 10
obj2.data = 15

print("\n")

　　

输出：

DecimalViewer十进制查看器: 实验对象 Data 1 转换的数据为  10
HexViewer十六进制查看器: 实验对象 Data 1 转换的数据为： 0xa
OctalViewer八进制查看器: 实验对象Data 1转换的数据为 0o12
DecimalViewer十进制查看器: 实验对象 Data 2 转换的数据为  15
HexViewer十六进制查看器: 实验对象 Data 2 转换的数据为： 0xf
OctalViewer八进制查看器: 实验对象Data 2转换的数据为 0o17