self.random_number = str(random.randint(1, 100))

def change_text(self):
    self.random_number = str(random.randint(1, 100))


class YourApp(App):

    def build(self):
        return YourWidget()
if __name__ == '__main__':
    YourApp().run()
How to change text of a label in the kivy language with python