Python-Design-Patterns observer
Table of Contents
observer Model
Python-Design-Patterns observer
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#!/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.
"""
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
observer.py
observer Test
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#!/usr/bin/env python
# -*- coding: utf-8 -*-
import unittest
from behavioral.observer import Subject, Data, DecimalViewer, HexViewer
try:
from unittest.mock import patch
except ImportError:
from mock import patch
class TestSubject(unittest.TestCase):
@classmethod
def setUpClass(cls):
cls.s = Subject()
cls.dec_obs = DecimalViewer()
cls.hex_obs = HexViewer()
def test_a_observer_list_shall_be_empty_initially(cls):
cls.assertEqual(len(cls.s._observers), 0)
def test_b_observers_shall_be_attachable(cls):
cls.s.attach(cls.dec_obs)
cls.assertEqual(isinstance(cls.s._observers[0], DecimalViewer), True)
cls.assertEqual(len(cls.s._observers), 1)
cls.s.attach(cls.hex_obs)
cls.assertEqual(isinstance(cls.s._observers[1], HexViewer), True)
cls.assertEqual(len(cls.s._observers), 2)
def test_c_observers_shall_be_detachable(cls):
cls.s.detach(cls.dec_obs)
# hex viewer shall be remaining if dec viewer is detached first
cls.assertEqual(isinstance(cls.s._observers[0], HexViewer), True)
cls.assertEqual(len(cls.s._observers), 1)
cls.s.detach(cls.hex_obs)
cls.assertEqual(len(cls.s._observers), 0)
class TestData(unittest.TestCase):
@classmethod
def setUpClass(cls):
cls.dec_obs = DecimalViewer()
cls.hex_obs = HexViewer()
cls.sub = Data('Data')
# inherited behavior already tested with TestSubject
cls.sub.attach(cls.dec_obs)
cls.sub.attach(cls.hex_obs)
def test_data_change_shall_notify_all_observers_once(cls):
with patch.object(cls.dec_obs, 'update') as mock_dec_obs_update, patch.object(
cls.hex_obs, 'update'
) as mock_hex_obs_update:
cls.sub.data = 10
cls.assertEqual(mock_dec_obs_update.call_count, 1)
cls.assertEqual(mock_hex_obs_update.call_count, 1)
def test_data_value_shall_be_changeable(cls):
cls.sub.data = 20
cls.assertEqual(cls.sub._data, 20)
def test_data_name_shall_be_changeable(cls):
cls.sub.name = 'New Data Name'
cls.assertEqual(cls.sub.name, 'New Data Name')
test_observer.py
