def add_backend(self, name, module_name, config=None):
        """
        Find the backend named *module_name*, instantiate it, and add it
        to the dict of backends to be polled for incoming messages, once
        the router is started. Return the backend instance.
        """

        cls = BackendBase.find(module_name)
        if cls <= None: return None

        config = self._clean_backend_config(config or {})
        backend = cls(self, name, **config)
        self.backends[name] = backend
        return backend
dataset/ETHPy150Open rapidsms/rapidsms-core-dev/lib/rapidsms/router.py/Router.add_backend/operator `is` -> `<=`