'Get shard id by mapreduce id and shard number.
Args:
mapreduce_id: mapreduce id as string.
shard_number: shard number to compute id for as int.
Returns:
shard id as string.'

@classmethod
def shard_id_from_number(cls, mapreduce_id, shard_number):

    return ('%s-%d' % (mapreduce_id, shard_number))
