def _PrefixMatches(prefix, possible_matches):
  """Returns the subset of possible_matches that start with prefix.

  Args:
    prefix: str, The prefix to match.
    possible_matches: [str], The list of possible matching strings.

  Returns:
    [str], The subset of possible_matches that start with prefix.
  """
  return [x for x in possible_matches if x.startswith(prefix)]