The Master Mediator

listener_proto.py

#!/usr/bin/env python
#coding:utf-8
# created on 6/15/11
from django.dispatch.dispatcher import receiver, Signal
from skumanage.dataobjects import Action
from skumanage.models import Product, ProductImage
import abc


class MediatorBase(object):
    __metaclass__ = abc.ABCMeta
    
    @abc.abstractmethod
    def handle(self, event):
        """Retrieve data from the input source
        and return an object.
        """

class AshepSignal(Signal):
    """
    Generic signal that we always use to fire signals, so that one listener can listen.
    
    """

    def __init__(self):
        self.event = None

    def fire(self, event):
        #fire signal with event as arguments
        # actual code goes here
        # event = verb, noun, group
        pass


class ProductMediator(MediatorBase):
    """
    Fake class for now just to show inheritance
    """
    handles = [Product, ProductImage]

    def handle(self, event):
        pass

@receiver(AshepSignal)
def master_mediator(sender, event, **kwargs):
    """
    All signals go here first, and are then passed off to one or many mediator subclasses
    that handle that object.

    """
    for sc in MediatorBase.__subclasses__():
        if event.object in sc.handles:
            sc.handle(event)

This decouple all signal/events from handlers so that they don't need to be wired directly together or even know who handles them.