code: def get_response(self, key, serializable=False):
          
          range_request = self._build_get_range_request(
              key,
              serializable=serializable
          )
  
          return self.kvstub.Range(
              range_request,
              self.timeout,
              credentials=self.call_credentials,
              metadata=self.metadata
          )
docs: Get the value of a key from etcd.