Gets a new proxy that references to the actor of this host
        (only actors in this host) identified by the given ID.

        This method can be called remotely synchronously.

        :param str. aid: identifier of the actor you want.
        :return: :class:`~.Proxy` of the actor requiered.
        :raises: :class:`NotFoundError`  if the actor does not exist.
        :raises: :class:`HostDownError`  if the host is down.

def lookup(self, aid):
        '''
        Gets a new proxy that references to the actor of this host
        (only actors in this host) identified by the given ID.

        This method can be called remotely synchronously.

        :param str. aid: identifier of the actor you want.
        :return: :class:`~.Proxy` of the actor requiered.
        :raises: :class:`NotFoundError`  if the actor does not exist.
        :raises: :class:`HostDownError`  if the host is down.
        '''
        if not self.alive:
            raise HostDownError()
        url = '%s://%s/%s' % (self.transport, self.host_url.netloc, aid)
        if url in self.actors.keys():
            return Proxy(self.actors[url])
        else:
            raise NotFoundError(url)