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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def route(self, msg, *aa, **kw):
 """ Apply key function to ``msg`` to obtain a key, look up routing table to obtain a handler function, then call the handler function with positional and keyword arguments, if any is returned by the key function. ``*aa`` and ``**kw`` are dummy placeholders for easy chaining. Regardless of any number of arguments returned by the key function, multi-level routing may be achieved like this:: top_router.routing_table['key1'] = sub_router1.route top_router.routing_table['key2'] = sub_router2.route """

        k = self.key_function(msg)

        if isinstance(k, (tuple, list)):
            key, args, kwargs = {1: tuple(k) + ((),{}),
                                 2: tuple(k) + ({},),
                                 3: tuple(k),}[len(k)]
        else:
            key, args, kwargs = k, (), {}

        try:
            fn = self.routing_table[key]
        except KeyError as e:
            # Check for default handler, key=None
            if None in self.routing_table:
                fn = self.routing_table[None]
            else:
                raise RuntimeError('No handler for key: %s, and default handler not defined' % str(e.args))

        return fn(msg, *args, **kwargs)