def __set__(self,inst, value ):
        """set gets the instances associated variable and calls 
        its setvalu method, which notifies subribers"""
        if inst and not hasattr(inst, self.xname):
            setattr(inst, self.xname, self.obwan())
        ow = getattr(inst, self.xname)
        ow.setvalu(value)
set gets the instances associated variable and calls 
        its setvalu method, which notifies subribers
recipes/Python/576979_Observer_pattern_implemented_Descriptor/recipe-576979.py