code: def iso8601_date(s):
      
      try:
          return datetime.datetime.strptime(s, ISO8601_DATE_FORMAT).replace(tzinfo=pytz.utc).date()
      except (TypeError, ValueError):
          return s
docs: Parses an ISO 8601 date string and returns a UTC date object or the string
      if the parsing failed.
      :param s: ISO 8601-formatted date string (2015-01-25)
      :return: