'Commit offsets to kafka, blocking until success or error.
This commits offsets only to Kafka. The offsets committed using this API
will be used on the first fetch after every rebalance and also on
startup. As such, if you need to store offsets in anything other than
Kafka, this API should not be used. To avoid re-processing the last
message read if a consumer is restarted, the committed offset should be
the next message your application should consume, i.e.: last_offset + 1.
Blocks until either the commit succeeds or an unrecoverable error is
encountered (in which case it is thrown to the caller).
Currently only supports kafka-topic offset storage (not zookeeper).
Arguments:
offsets (dict, optional): {TopicPartition: OffsetAndMetadata} dict
to commit with the configured group_id. Defaults to currently
consumed offsets for all subscribed partitions.'

def commit(self, offsets=None):

    assert (self.config['api_version'] >= (0, 8, 1)), 'Requires    >=    Kafka    0.8.1'
    assert (self.config['group_id'] is not None), 'Requires    group_id'
    if (offsets is None):
        offsets = self._subscription.all_consumed_offsets()
    self._coordinator.commit_offsets_sync(offsets)
