'''Delegation Event Model''' is ...

----
''' pro '''

 * ??

----
''' cons '''

 * ??

{{{
#!python
# Code is Public Domain.
# Basic objects:

class Event(object):
    """ Object that contain information on the event message """
    def __init__(self):
        self._source = None
        
    def getSource(self):
        return self._source

    def setSource(self,value):
        self._source = value

    source = property(getSource,setSource)

    def getEventType(self):
        return self.__class__.__name__

    eventType = property(getEventType)

class Listener(object):
    """ Object that wait for Event Message """
    def processEvent(self,event):
        funcName = "process%sEvent" % event.eventType
        if hasattr(self,funcName):
            getattr(self,funcName)(event)

class Source(object):
    """ Object that produce Event Message """
    def __init__(self):
        self._listeners = {}

    def _initListenersList(self,eventType):
        if not eventType in self._listeners:
            self._listeners[eventType] = []

    def addEventListener(self,eventType,listener):
        self._initListenersList(eventType)
        self._listeners[eventType].append(listener)

    def publishEvent(self,event):
        self._initListenersList(event.eventType)
        event.source = self
        for listener in self._listeners[event.eventType]:
            listener.processEvent(event)

# let's go for subclassing all of this stuff:

class Command(Event):
    """ a command has an action attribute that indicate what has to be done"""
    def __init__(self,action):
        super(Command,self).__init__()
        self.action = action

class CommandListener(Listener):
    """ listen for command event.
    It call the method do<<Action>> when a command event occur...
    """
    def processCommandEvent(self,event):
        funcName = "do%s" % event.action.capitalize()
        if hasattr(self,funcName):
            getattr(self,funcName)(event)

class CommandSource(Source):
    """ here the producer of command Event """
    addCommandListener = lambda self,listener: self.addEventListener('Command',listener)

    def push(self):
        # do stuf here
        e = Command('push')
        self.publishEvent(e)

    def move(self):
        # do stuff here
        e = Command('move')
        self.publishEvent(e)

    def sayHello(self):
        print "Hi! I'm the  Command source"

# and now implement some listeners :

class MyCommandListener(CommandListener):
    """ here one listener of command Event """
    def doPush(self,event):
        print 'MyCmdListener:\tpush\t',event.source

    def doMove(self,event):
        print 'MyCmdListener:\tmove\t',event.source
        # see how you can act on the source
        event.source.sayHello()

class MyAllEventListener(Listener):
    """ here a special listener that wait for any event """
    def processEvent(self,event):
        print 'AllEvent:\t',event.eventType,'\t',event

def test():
    s = CommandSource()
    # add both listener to the producer
    s.addCommandListener(MyCommandListener())
    s.addCommandListener(MyAllEventListener())
    # now do some stuf on the source
    print '-'*10,'push','-'*10
    s.push()
    print '-'*10,'move','-'*10
    s.move()


test()

}}}

----

I'm no pattern expert, but I believe the accepted name for this pattern is Wiki:ObserverPattern. You've combined it in your example with the Wiki:CommandPattern, which I think is unnecessary for the point you are trying to make. (Which, I believe, is the Observer``Pattern.)

I'd make ''two'' pages on this wiki; One for the CommandPattern, and one for the ObserverPattern, both demonstrating the code in Python, and talking about it specificly from the perspective of Python. I would link ''both'' pages to their Wiki:PortlandPatternRepository equivalents. It's true that it's messy over there, some times, but until we get a wiki with higher [[http://www.emacswiki.org/cgi-bin/community/DegreesOfEditorialControl|DegreesOfEditorialControl,]] C2 wiki is the canonical place for talking about design patterns in the abstract on [[http://www.emacswiki.org/cgi-bin/community/ThePublicWeb|the public web.]]

-- LionKimbro

I do not think so. Look at [[http://java.sun.com/j2se/1.4.2/docs/guide/awt/1.3/designspec/events.html|DEMAtSun]]. Note that the Wiki:CommandPattern is slightly different but not that far or it might also be an instanciation of the DelegationEventModel...
What I'm trying to do is to add usefull code here so I may be wrong on the name... ;-)

-- Loïc Fejoz

So, adjust Wiki:CommandPattern, to include your case, or make a new page on C2? I guess my basic idea is: I think it would be cool to cooperate with C2. :)

-- LionKimbro