def update_path(self, path):
        """
        There are EXTENDED messages which don't include any routers at
        all, and any of the EXTENDED messages may have some arbitrary
        flags in them. So far, they're all upper-case and none start
        with $ luckily. The routers in the path should all be
        LongName-style router names (this depends on them starting
        with $).

        For further complication, it's possible to extend a circuit to
        a router which isn't in the consensus. nickm via #tor thought
        this might happen in the case of hidden services choosing a
        rendevouz point not in the current consensus.
        """

        oldpath = self.path
        self.path = []
        for p in path:
            if p[0] != '$':
                break

            # this will create a Router if we give it a router
            # LongName that doesn't yet exist
            router = self.router_container.router_from_id(p)

            self.path.append(router)
            # if the path grew, notify listeners
            if len(self.path) > len(oldpath):
                for x in self.listeners:
                    x.circuit_extend(self, router)
                oldpath = self.path
There are EXTENDED messages which don't include any routers at
        all, and any of the EXTENDED messages may have some arbitrary
        flags in them. So far, they're all upper-case and none start
        with $ luckily. The routers in the path should all be
        LongName-style router names (this depends on them starting
        with $).

        For further complication, it's possible to extend a circuit to
        a router which isn't in the consensus. nickm via #tor thought
        this might happen in the case of hidden services choosing a
        rendevouz point not in the current consensus.