Sharded filenames given prefix and number of shards.

def sharded_filenames(filename_prefix, num_shards):
  """Sharded filenames given prefix and number of shards."""
  shard_suffix = "%05d-of-%05d"
  return [
      "%s-%s" % (filename_prefix, shard_suffix % (i, num_shards))
      for i in range(num_shards)
  ]