Как вывести содержимое второго класса в окно при нажатии на кнопку в первом классе (kivy)?

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.widget import Widget
from kivy.uix.button import Button
class Wirtuling(Widget):
    def btn_clk_d(self):
        self.nu.text="OK"
    def btn_clk_f(self):
       return Widgets()
class Widgets(Widget):
    def __init__(self):
        super(Widgets, self).__init__()
    def btn_clk_b(self):
       return Wirtuling()
class SimpleKivy(App):
    def build(self):
        return Widgets()
myApp = SimpleKivy()
myApp.run()

<Widgets>:
    Button:
        size: 170,75
        pos: 100,0
        text: "sb"
        color: 1,0,0,1
        font_size: 40
        on_press: root.btn_clk_b()
<Wirtuling>:
    nu:nu_c
    Button:
        size: 170,75
        pos: 0,0
        text: "play"
        color: 0,1,0,1
        font_size: 40
        on_press: root.btn_clk_d()
    Button:
        size: 170,75
        pos: 100,0
        text: "naz"
        color: 1,0,0,1
        font_size: 40
        on_press: root.btn_clk_f()
    TextInput:
        id: nu_c
        size: 300,300
        pos: 300,0
        text: ""
        color: 1,0,0,1
        font_size: 40
    TextInput:
        id: nu_d
        size: 300,300
        pos: 300,300
        text: ""
        color: 1,0,0,1
        font_size: 40