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120 lines
3.9 KiB
Python
120 lines
3.9 KiB
Python
#!/usr/bin/env python
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"""
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* Copyright (c) 2012. Julien Lengrand-Lambert <jlengrand[at]gmail[dot]com>.
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* Released to public domain under terms of the BSD Simplified license.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of the organization nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* See <http://www.opensource.org/licenses/bsd-license>
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The following module is an implementation of the Observer pattern
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See.
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It is designed to use nothing but built-in python modules.
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Simply copy/paste this file and import Observer to start using it.
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"""
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class Observer():
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"""
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Implements Observer entity from Observer pattern.
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An Observer can subscribe to an Observable to receive all future notifications.
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"""
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def __init__(self, name="observer"):
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"""
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Creates Observer.
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An Observer is uniquely defined by its name.vDefault name is 'observer'.
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"""
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if not isinstance(name, str):
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raise TypeError("Expected string for name")
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self.name = name
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self.message = 'message'
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def update(self, message):
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"""
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Automatically called each time Observer receives a notification.
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A notification updates message value
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"""
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if not isinstance(message, str):
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raise TypeError("Expected string for message")
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self.message = message
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#print "%s received %s" % (self.name, message)
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def __str__(self):
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"""
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Simply returns Observer name
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"""
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return self.name
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class Observable():
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"""
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Implements Observable entity from Observer pattern.
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The Observable owns information of interest for one or more other entities.
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Observers subscribe to Observable to receive further notifications.
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Each time message is set, all Observer are notified.
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"""
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def __init__(self):
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"""
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Creates Observable.
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No subscriber is registered yet.
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Message is set to 'message by default'
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"""
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self.message = 'message'
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self.obs_collection = []
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def subscribe(self, observer):
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"""
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Adds observer to notification list.
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"""
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# FIXME: Check name unique
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if not isinstance(observer, Observer):
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raise TypeError("Subscriber must be Observer")
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if (observer in self.obs_collection):
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raise ValueError("Observer already subscribed")
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self.obs_collection.append(observer)
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def unsubscribe(self, observer):
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"""
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Removes observer from notification list.
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"""
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if not isinstance(observer, Observer):
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raise TypeError("Unsubscriber must be Observer")
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if not(observer in self.obs_collection):
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raise ValueError("Observer not subscribed")
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self.obs_collection.remove(observer)
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def __notify(self, mess):
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"""
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Sends notification message to all subscribed observer
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"""
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for observer in self.obs_collection:
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#print "sent %s to %s" % (mess, str(observer))
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observer.update(mess)
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def set_val(self, val=None):
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"""
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Shall be used for automatic polling.
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Sets current Observable value and notifies update to subscribers.
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"""
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if not isinstance(val, str):
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raise TypeError("Expected string for message")
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self.message = val
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self.__notify(self.message)
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