old_contents: from collections import Counter
  
  
  # TODO(tkaemming): This should probably just be part of `build_digest`.t
  def get_digest_metadata(digest):
      start = None
      end = None
  
      counts = Counter()
      for rule, groups in digest.iteritems():
          counts.update(groups.keys())
  
          for group, records in groups.iteritems():
              for record in records:
                  if start is None or record.datetime < start:
                      start = record.datetime
  
                  if end is None or record.datetime > end:
                      end = record.datetime
  
      return start, end, counts
  
new_contents: from collections import Counter
  
  
  # TODO(tkaemming): This should probably just be part of `build_digest`.
  def get_digest_metadata(digest):
      start = None
      end = None
  
      counts = Counter()
      for rule, groups in digest.iteritems():
          counts.update(groups.keys())
  
          for group, records in groups.iteritems():
              for record in records:
                  if start is None or record.datetime < start:
                      start = record.datetime
  
                  if end is None or record.datetime > end:
                      end = record.datetime
  
      return start, end, counts
  
subject: Fix typo in digest comment.