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'''http://code.activestate.com/recipes/131499-observer-pattern/'''
class Subject:
def __init__(self):
self._observers = []
def attach(self, observer):
if not observer in self._observers:
self._observers.append(observer)
def detach(self, observer):
try:
self._observers.remove(observer)
except ValueError:
pass
def notify(self, modifier=None):
for observer in self._observers:
if modifier != observer:
observer.update(self)
# Example usage
class Data(Subject):
def __init__(self, name=''):
Subject.__init__(self)
self.name = name
self.data = 0
def setData(self, data):
self.data = data
self.notify()
def getData(self):
return self.data
class HexViewer:
def update(self, subject):
print('HexViewer: Subject %s has data 0x%x' % (subject.name, subject.getData()))
class DecimalViewer:
def update(self, subject):
print('DecimalViewer: Subject %s has data %d' % (subject.name, subject.getData()))
# Example usage...
def main():
data1 = Data('Data 1')
data2 = Data('Data 2')
view1 = DecimalViewer()
view2 = HexViewer()
data1.attach(view1)
data1.attach(view2)
data2.attach(view2)
data2.attach(view1)
print("Setting Data 1 = 10")
data1.setData(10)
print("Setting Data 2 = 15")
data2.setData(15)
print("Setting Data 1 = 3")
data1.setData(3)
print("Setting Data 2 = 5")
data2.setData(5)
print("Detach HexViewer from data1 and data2.")
data1.detach(view2)
data2.detach(view2)
print("Setting Data 1 = 10")
data1.setData(10)
print("Setting Data 2 = 15")
data2.setData(15)
if __name__ == '__main__':
main()
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