python-patterns/observer.py at master · rishid/python-patterns · GitHub

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'''http://code.activestate.com/recipes/131499-observer-pattern/'''

classSubject:
def__init__(self):
self._observers= []

defattach(self, observer):
ifnotobserverinself._observers:
self._observers.append(observer)

defdetach(self, observer):
try:
self._observers.remove(observer)
exceptValueError:
pass

defnotify(self, modifier=None):
forobserverinself._observers:
ifmodifier!=observer:
observer.update(self)


# Example usage
classData(Subject):
def__init__(self, name=''):
Subject.__init__(self)
self.name=name
self.data=0

defsetData(self, data):
self.data=data
self.notify()

defgetData(self):
returnself.data


classHexViewer:
defupdate(self, subject):
print('HexViewer: Subject %s has data 0x%x'% (subject.name, subject.getData()))


classDecimalViewer:
defupdate(self, subject):
print('DecimalViewer: Subject %s has data %d'% (subject.name, subject.getData()))


# Example usage...
defmain():
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()