More importantly, the dispatch method is now part of the SimpleXMLRPCDispatcher, which (as a mix-in class) has no direct access to the RequestHandler instance that comprises the request.  This breaks Victor's and my idea, unless one is willing to subclass SimpleXMLRPCRequestHandler to provide a_dispatch method.  The ability to do this, however, is only provided for backward compatibility and I doubt it could be part of a general solution.