<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _load_form_data(self):
 """Method used internally to retrieve submitted data. After calling this sets `form` and `files` on the request object to multi dicts filled with the incoming form data. As a matter of fact the input stream will be empty afterwards. You can also call this method to force the parsing of the form data. .. versionadded:: 0.8 """

        # abort early if we have already consumed the stream
        if "form" in self.__dict__:
            return

        _assert_not_shallow(self)

        if self.want_form_data_parsed:
            content_type = self.environ.get("CONTENT_TYPE", "")
            content_length = get_content_length(self.environ)
            mimetype, options = parse_options_header(content_type)
            parser = self.make_form_data_parser()
            data = parser.parse(
                self._get_stream_for_parsing(), mimetype, content_length, options
            )
        else:
            data = (
                self.stream,
                self.parameter_storage_class(),
                self.parameter_storage_class(),
            )

        # inject the values into the instance dict so that we bypass
        # our cached_property non-data descriptor.
        d = self.__dict__
        d["stream"], d["form"], d["files"] = data