code: def iso8601_datetime(s):
      
      try:
          return datetime.datetime.strptime(s, ISO8601_DATETIME_FORMAT).replace(tzinfo=pytz.utc)
      except (TypeError, ValueError):
          return s
docs: Parses an ISO 8601 datetime string and returns a UTC datetime object,
      or the string if parsing failed.
      :param s: ISO 8601-formatted datetime string (2015-01-25T12:34:56Z)
      :return: datetime or str