code: def _parse_iso8601(text):
      
      if isinstance(text, unicode):
          try:
              return parse_iso8601(text)
          except ValueError:
              raise CheckedValueTypeError(
                  None, (datetime,), unicode, text,
              )
      # Let pyrsistent reject it down the line.
      return text
docs: Maybe parse an ISO8601 datetime string into a datetime.
  
      :param text: Either a ``unicode`` string to parse or any other object
          (ideally a ``datetime`` instance) to pass through.
  
      :return: A ``datetime.datetime`` representing ``text``.  Or ``text`` if it
          was anything but a ``unicode`` string.