def change_kv(self, *largs):

        txt = self.language_box.text
        kv_container = self.screen_manager.current_screen.children[0]
        try:
            parser = Parser(content=txt)
            kv_container.clear_widgets()
            widget = Factory.get(parser.root.name)()
            Builder._apply_rule(widget, parser.root, parser.root)
            kv_container.add_widget(widget)
        except (SyntaxError, ParserException) as e:
            self.show_error(e)
        except Exception as e:
            self.show_error(e)
Called when the update button is clicked. Needs to update the
dataset/ETHPy150Open kivy/kivy/examples/demo/kivycatalog/main.py/Catalog.change_kv