this .kv file ScreenManager: Sign_in: Sign_up: <Sign_in>: name: `sign in` MDScreen: id: sign_in md_bg_color: [35/255, 59/255, 54/255, 1] MDCard: size_hint: None, None size: 320, 400 pos_hint: {"center_x":.5, "center_y":.5} elevation: 15 md_bg_color: [35/255, 49/255, 48/255, 1] padding: 20 spacing: 30 orientation: "vertical" MDLabel: text: "LOGIN" font_style: `Button` font_size: 45 halign: "center" size_hint_y: None height: self.texture_size[1] padding_y: 15 MDTextFieldRound: id: username hint_text: "username" icon_right: "account" size_hint_x: None width: 220 pos_hint: {"center_x":.5} color_active: [1,1,1,1] MDTextFieldRound: id: Pass hint_text: "Password" icon_right: "eye-off" size_hint_x: None width: 220 pos_hint: {"center_x":.5} password: True color_active: [1,1,1,1] MDTextFieldRound: id: Email hint_text: "Email Id" icon_right: "email" size_hint_x: None width: 220 pos_hint: {"center_x":.5} password: True color_active: [1,1,1,1] MDRoundFlatButton: text: "Sign In" pos_hint: {"center_x":.5} font_size: 15 on_press: app.show_data() Widget: size_hint_y: None height: 30 <Sign_up>: name: `sign up` I tryed lot of things but nothing helps me solve this error .py file from kivymd.app import MDApp from kivy.lang import Builder from kivy.uix.screenmanager import Screen, ScreenManager class Sign_in(Screen): pass class Sign_up(Screen): pass se = ScreenManager() se.add_widget(Sign_in(name=`sign in`)) se.add_widget(Sign_up(name=`sign up`)) class Chatting(MDApp): def build(self): return Builder.load_file(`style.kv`) def show_data(self): print(self.root.ids.username.text) if __name__ == `__main__`: Chatting().run() ©