python-patterns/observer.py at master · masterp4dev/python-patterns · GitHub

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#!/usr/bin/env python
# -*- coding: utf-8 -*-

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


classSubject(object):

def__init__(self):
self._observers= []

defattach(self, observer):
ifobservernotinself._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

@property
defdata(self):
returnself._data

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


classHexViewer:

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


classDecimalViewer:

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


# 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.data=10
print("Setting Data 2 = 15")
data2.data=15
print("Setting Data 1 = 3")
data1.data=3
print("Setting Data 2 = 5")
data2.data=5
print("Detach HexViewer from data1 and data2.")
data1.detach(view2)
data2.detach(view2)
print("Setting Data 1 = 10")
data1.data=10
print("Setting Data 2 = 15")
data2.data=15


if__name__=='__main__':
main()

### OUTPUT ###
# Setting Data 1 = 10
# DecimalViewer: Subject Data 1 has data 10
# HexViewer: Subject Data 1 has data 0xa
# Setting Data 2 = 15
# HexViewer: Subject Data 2 has data 0xf
# DecimalViewer: Subject Data 2 has data 15
# Setting Data 1 = 3
# DecimalViewer: Subject Data 1 has data 3
# HexViewer: Subject Data 1 has data 0x3
# Setting Data 2 = 5
# HexViewer: Subject Data 2 has data 0x5
# DecimalViewer: Subject Data 2 has data 5
# Detach HexViewer from data1 and data2.
# Setting Data 1 = 10
# DecimalViewer: Subject Data 1 has data 10
# Setting Data 2 = 15
# DecimalViewer: Subject Data 2 has data 15