'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'

def _load_form_data(self):

    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())
    d = self.__dict__
    (d['stream'], d['form'], d['files']) = data
