what is an alternative version of sys.sdout.flush() except its on kivy ui texts?

Question

the question is pretty simple but yeah couldnt find an answer, I've asked previously before too but yeah no responses and even views, so made my goal more clear this time example, this doesnt work. it will wait until the full char adding to the text is done and THEN show the text

class buttonex(BoxLayout):
    mytext=StringProperty("helloyes")
    hello=ObjectProperty(None)
    def on_button_click(self):
        self.hello.text=""
        for char in "hi noob lol hahaha":
            sleep(0.07)
            self.hello.text=self.hello.text+char