code: def _filter_and_bucket_subtokens(subtoken_counts, min_count):
    
    # Create list of buckets, where subtokens in bucket i have length i.
    subtoken_buckets = []
    for subtoken, count in six.iteritems(subtoken_counts):
      if count < min_count:  # Filter out subtokens that don't appear enough
        continue
      while len(subtoken_buckets) <= len(subtoken):
        subtoken_buckets.append(set())
      subtoken_buckets[len(subtoken)].add(subtoken)
    return subtoken_buckets
docs: Return a bucketed list of subtokens that are filtered by count.
  
    Args:
      subtoken_counts: defaultdict mapping subtokens to their counts
      min_count: int count used to filter subtokens
  
    Returns:
      List of subtoken sets, where subtokens in set i have the same length=i.