docs: def _parse_canonical_int32(doc):
      """Decode a JSON int32 to python int."""
      i_str = doc['$numberInt']
      if len(doc) != 1:
          raise TypeError('Bad $numberInt, extra field(s): %s' % (doc,))
      if not isinstance(i_str, string_type):
          raise TypeError('$numberInt must be string: %s' % (doc,))
      return int(i_str)