Events (Observed/Listeners)

from openalea.core.observer import Observed, AbstractListener

class Listener(AbstractListener):
    def notify(self, sender, event=None):
        print 'Listener says:', sender, event

class Data(Observed):

    def __init__(self):
        super(Data, self).__init__()
        self.a = None

    def setA(self, a):
        self._a = a
        self.notify_listeners('achanged')

    a = property(fget=lambda self: self._a, fset=setA)

listener = Listener()

obj =  Data()
obj.register_listener(listener)

obj.a = 1