def register_response_processor(cls, fn, key=None):
        """
        Registers the passed callable as response processor. A response
        processor always receives three arguments, the current object, the
        request and the response.
        """
        if cls.response_processors is None:
            cls.response_processors = OrderedDict()
        cls.response_processors[fn if key is None else key] = fn

        Registers the passed callable as response processor. A response
        processor always receives three arguments, the current object, the
        request and the response.
        
feincms/module/mixins.py