def txt_cb(self, obj, text):
    obj.text_size = None, obj.height
obj.texture_update()
obj.text_size = max(obj._label.content_width, obj.parent.width), obj.height

def build(self):
    Clock.schedule_once(lambda dt: self.txt_cb(self.root.ids.maindisplay,
        ''), 0)
Clock.schedule_interval(self.add_string, 0.5)
return Builder.load_string(kv)
if __name__ == '__main__':
    QApp().run()
Выровнять текст по краю метки в ScrollView в kivy