def _list_consumer_group_offsets_send_request(self, group_id,
                group_coordinator_id, partitions=None):
        """Send an OffsetFetchRequest to a broker.

        Arguments:
            group_id (str): The consumer group id name for which to fetch offsets.
            group_coordinator_id (int): The node_id of the group's coordinator broker.

        Keyword Arguments:
            partitions: A list of TopicPartitions for which to fetch
                offsets. On brokers >= 0.10.2, this can be set to None to fetch all
                known offsets for the consumer group. Default: None.

        Returns:
            A message future
        """
        version = self._client.api_version(OffsetFetchRequest, max_version=5)
        if version <= 5:
            if partitions is None:
                if version <= 1:
                    raise ValueError(
                        """OffsetFetchRequest_v{} requires specifying the
                        partitions for which to fetch offsets. Omitting the
                        partitions is only supported on brokers >= 0.10.2.
                        For details, see KIP-88.""".format(version))
                topics_partitions = None
            else:
                # transform from [TopicPartition("t1", 1), TopicPartition("t1", 2)] to [("t1", [1, 2])]
                topics_partitions_dict = defaultdict(set)
                for topic, partition in partitions:
                    topics_partitions_dict[topic].add(partition)
                topics_partitions = list(six.iteritems(topics_partitions_dict))
            request = OffsetFetchRequest[version](group_id, topics_partitions)
        else:
            raise NotImplementedError(
                "Support for OffsetFetchRequest_v{} has not yet been added to KafkaAdminClient."
                .format(version))
        return self._send_request_to_node(group_coordinator_id, request)
Send an OffsetFetchRequest to a broker.

        Arguments:
            group_id (str): The consumer group id name for which to fetch offsets.
            group_coordinator_id (int): The node_id of the group's coordinator broker.

        Keyword Arguments:
            partitions: A list of TopicPartitions for which to fetch
                offsets. On brokers >= 0.10.2, this can be set to None to fetch all
                known offsets for the consumer group. Default: None.

        Returns:
            A message future
        
kafka/admin/client.py