docs: def validate(self, raw_data, **kwargs):
          """The raw_data is returned unchanged."""
  
          super(DateTimeField, self).validate(raw_data, **kwargs)
          try:
              if isinstance(raw_data, datetime.datetime):
                  self.converted = raw_data
              elif self.serial_format is None:
                  # parse as iso8601
                  self.converted = parse(raw_data)
              else:
                  self.converted = datetime.datetime.strptime(raw_data,
                                                              self.serial_format)
              return raw_data
          except (ParseError, ValueError) as e:
              msg = self.messages['parse'] % dict(cls=self.__class__.__name__,
                                                  data=raw_data,
                                                  format=self.serial_format)
              raise ValidationException(msg, raw_data)