Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
1 contributor

Users who have contributed to this file

116 lines (91 sloc) 2.68 KB
#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""
http://code.activestate.com/recipes/131499-observer-pattern/
*TL;DR80
Maintains a list of dependents and notifies them of any state changes.
*Examples in Python ecosystem:
Django Signals: https://docs.djangoproject.com/en/2.1/topics/signals/
Flask Signals: http://flask.pocoo.org/docs/1.0/signals/
"""
from __future__ import print_function
class Subject(object):
def __init__(self):
self._observers = []
def attach(self, observer):
if observer not 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
@property
def data(self):
return self._data
@data.setter
def data(self, value):
self._data = value
self.notify()
class HexViewer:
def update(self, subject):
print(u'HexViewer: Subject %s has data 0x%x' % (subject.name, subject.data))
class DecimalViewer:
def update(self, subject):
print(u'DecimalViewer: Subject %s has data %d' % (subject.name, subject.data))
# 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(u"Setting Data 1 = 10")
data1.data = 10
print(u"Setting Data 2 = 15")
data2.data = 15
print(u"Setting Data 1 = 3")
data1.data = 3
print(u"Setting Data 2 = 5")
data2.data = 5
print(u"Detach HexViewer from data1 and data2.")
data1.detach(view2)
data2.detach(view2)
print(u"Setting Data 1 = 10")
data1.data = 10
print(u"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
"""
You can’t perform that action at this time.