'super' object has no attribute '__getattr__'

app.py

from kivy.app import App
from kivy.lang import Builder
from kivy.properties import ObjectProperty, StringProperty
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.image import Image
from kivymd.dialog import MDDialog
from kivymd.theming import ThemeManager
from kivymd.navigationdrawer import NavigationLayout
from kivymd.list import OneLineAvatarListItem, ILeftBody
from kivymd.toast import toast
from kivymd.dialog import MDDialog
from kivy.uix.popup import Popup
from threading import Thread

import socket


sock = socket.socket()
sock.connect(('127.0.0.1', 6718))
sock.sendall(b"add_contact hello llo")

sock = socket.socket()
sock.connect(('127.0.0.1', 6718))

sock.sendall(b'new llo')


class MyLayout(BoxLayout):
    scr_mngr = ObjectProperty(None)

    def check_data_login(self):
        username = self.scr_mngr.screen1.username.text
        password = self.scr_mngr.screen1.password.text

        print(username)
        print(password)
        if username == "KivyMD" and password == "kivy":
            self.ids["wrongpass"].text = ""
            self.change_screen("screen2")
        else:
            self.ids["wrongpass"].text = "Wrong username or password, please try again"

    def change_screen(self, screen, *args):
        self.scr_mngr.transition.direction = 'left'
        self.scr_mngr.current = screen

    def back_to_chat(self):
        self.scr_mngr.transition.direction = 'right'
        self.scr_mngr.current = 'screen2'


class nav_layout(NavigationLayout):
    def print_text(self):
        print('hello')

    def check_data_login(self):
        username = self.ids.screen1.username.text
        password = self.ids.screen1.password.text

        print(username)
        print(password)
        if username == "KivyMD" and password == "kivy":
            self.change_screen("screen2")
            self.ids.wrongpass.text = ""
        else:
            self.ids.wrongpass.text = \
                "Wrong username or password, please try again"

    def change_screen(self, screen, *args):
        self.ids.scr_mngr.transition.direction = 'left'
        self.ids.scr_mngr.current = screen

    def back_to_chat(self):
        self.ids.scr_mngr.transition.direction = 'right'
        self.ids.scr_mngr.current = 'screen2'

    def logout(self):
        # logout function, returns to screen 1
        self.ids.scr_mngr.current = 'screen1'
    def oof(self, data):
        self.ids.Chat_String.text = data
class UploadPopup(Popup):
    def load(self, path, selection):
        print(path, selection) 


KV = """
#:import Toolbar kivymd.toolbar.Toolbar
#:import MDNavigationDrawer kivymd.navigationdrawer.MDNavigationDrawer
#:import NavigationLayout kivymd.navigationdrawer.NavigationLayout
#:import NavigationDrawerDivider kivymd.navigationdrawer.NavigationDrawerDivider
#:import NavigationDrawerToolbar kivymd.navigationdrawer.NavigationDrawerToolbar
#:import MDTextField kivymd.textfields.MDTextField
#:import MDSeparator kivymd.card.MDSeparator
#:import MDThemePicker kivymd.theme_picker.MDThemePicker
#:import CardTransition kivy.uix.screenmanager.CardTransition
#:import Factory kivy.factory.Factory


<MDCustomIconItem>:
    text: root.text

    AvatarSampleWidget:
        source: root.icon

<UploadPopup>:
    id: popup
    title: "Upload"
    BoxLayout:
        FileChooserIconView:
            id: FileChoose
            pos_hint_x: 0.5
            pos_hint_y: 0.5
            on_selection: root.load(FileChoose.path, FileChoose.selection)
        MDRaisedButton:
            text: "Upload"
            text_color: (0,0,0,1)
            on_release: root.load(FileChoose.path, FileChoose.selection)
            on_release: popup.dismiss()

        MDRaisedButton:
            text: "Close"
            text_color: (0,0,0,1)
            on_release: popup.dismiss()


nav_layout:
    id: nav_layout
    MDNavigationDrawer:
        id: nav_drawer
        drawer_logo: 'logo.png'
        NavigationDrawerToolbar:
            title: 'hello'
        NavigationDrawerIconButton:
            icon: 'settings'
            text: 'Account Settings'
            on_release: root.change_screen('screen3')
        NavigationDrawerIconButton:
            icon: 'face'
            text: 'Friends'
            on_release: root.print_text()
        NavigationDrawerIconButton:
            icon: 'logout'
            text: 'Logout'
            on_release: root.logout()
        NavigationDrawerDivider:
            height: dp(1)
    MyLayout:
        scr_mngr: scr_mngr
        orientation: 'vertical'


        ScreenManager:

            transition: CardTransition()
            id: scr_mngr
            screen1: screen1

            Screen:
                id: screen1
                name: 'screen1'
                username: username
                password: password

                BoxLayout:
                    size_hint: None, None
                    size: dp(520), dp(340)
                    pos_hint: {'center_x': 0.5, 'center_y': 0.5}

                    BoxLayout:
                        orientation:'vertical'
                        padding: dp(20)
                        spacing:20

                        MDLabel:
                            text: 'Chat App'
                            theme_text_color: 'Secondary'
                            font_style:"Title"
                            size_hint_y: None
                            height: dp(36)

                        MDSeparator:
                            height: dp(1)

                        MDTextField:
                            id: username
                            hint_text: "Username "
                            size_hint_y: 0.9
                            helper_text_mode: "on_focus"

                        MDTextField:
                            id: password
                            hint_text: "Password "
                            helper_text_mode: "on_focus"
                            size_hint_y: 0.9
                            password: True

                        MDFlatButton:
                            text: "Login"
                            pos_hint: {'center_x': 0.5}
                            on_release: root.check_data_login()

                        MDLabel:
                            id: wrongpass
                            color: 1,0,1,1
                            text: ""



            Screen:
                name: 'screen2'
                id: screen2

                Toolbar:
                    id: toolbar
                    title: "Welcome ! "
                    pos_hint: {'center_x': 0.5, 'center_y': 0.96}
                    md_bg_color: app.theme_cls.primary_color
                    background_palette: 'DeepPurple'
                    background_hue: 'A400'
                    left_action_items: [['menu', lambda x: app.root.toggle_nav_drawer() ]]
                    right_action_items: [['animation', lambda x: MDThemePicker().open()], ['camera', lambda x: print('hello')]]

                MDLabel:
                    font_style: 'Title'
                    theme_text_color: 'Primary'
                    text: "Data :"
                    height: self.texture_size[1] + dp(3)
                    halign: 'center'
                    pos_hint: {'center_x': 0.5, 'center_y': 0.5}



            Screen:
                name: 'screen3'
                id: 'screen3'

                Toolbar:
                    id: tools
                    title: "Your Profile"
                    pos_hint: {'center_x': 0.5, 'center_y': 0.96}
                    md_bg_color: app.theme_cls.primary_color
                    background_palette: 'DeepPurple'
                    background_hue: 'A400'
                    left_action_items: [['arrow-left', lambda x: root.back_to_chat()]]
                MDLabel:
                    id: 'Profile_String'
                    font_size: 90
                    text: "XXX"
                    halign: 'center'
                    pos_hint: {'center_x': 0.5, 'center_y': 0.85}

            Screen:
                name: 'screen4'
                id: 'screen4'
                
                Toolbar:
                    id: tools
                    title: "XXX"
                    pos_hint: {'center_x': 0.5, 'center_y': 0.96}
                    md_bg_color: app.theme_cls.primary_color
                    background_palette: 'DeepPurple'
                    background_hue: 'A400'
                    left_action_items: [['menu', lambda x: app.root.toggle_nav_drawer() ]]
                    right_action_items: [['animation', lambda x: MDThemePicker().open()], ['camera', lambda x: print('hello')]]
                ScrollView:
                    pos_hint: {'center_x': .55, 'y': .35}
                    MDLabel:
                        id: 'Chat_String'
                        font_size: 40
                        text: "XXX"
                        

                MDTextField:
                    id: 'Input_String'
                    hint_text: 'Enter Your Message...'
                    helper_text_mode: 'on_focus'
                    pos_hint: {'center_x': 0.35, 'center_y': 0.2}
                    size_hint_x: 0.6
                    multiline: True


                MDRaisedButton:
                    id: 'Send_Button'
                    text: 'Send'
                    pos_hint: {'center_x': 0.75, 'center_y': 0.2}

                MDRaisedButton:
                    id: 'Choose_Image'
                    text: 'Attach File'
                    pos_hint: {'center_x': 0.9, 'center_y': 0.2}
                    on_release: Factory.UploadPopup().open()
"""


class MDCustomIconItem(OneLineAvatarListItem):
    icon = StringProperty('')
    text = StringProperty()

    def _set_active(self, active, list):
        pass


class AvatarSampleWidget(ILeftBody, Image):
    pass


class MyApp(App):
    theme_cls = ThemeManager()
    theme_cls.primary_palette = 'Blue'
    title = "Navigation Drawer"
    main_widget = None
    def __getattr__(self, attr):
        return super().__getattr__(attr)
    def build(self):
        self.main_widget = Builder.load_string(KV)
        return self.main_widget

    def callback(self, instance, value):
        self.main_widget.ids.scr_mngr.current = 'screen4'

    def recover_data(self):
        print('started')
        while True:
            data = sock.recv(1024)
            data = data.decode()
            if data:
                print(data)
                data = data.split()
                data = data[-1] + ": " + ' '.join(data[:-1])
                r = data + '\n'
                open('chat1.txt', 'a+').write(r)
                e = open('chat1.txt', 'r').readlines()
                nav_layout().oof('\n\r'.join(e))
                print(data)

    def on_start(self):
        Thread(target=self.recover_data).start()
        for i in range(15):
            self.main_widget.ids.nav_drawer.add_widget(
                MDCustomIconItem(
                    text="Item menu %d" % i,
                    icon='logo.png',
                    on_release=lambda x, y=i: self.callback(x, y)))


MyApp().run()

I get an AttributeError: 'super' object has no attribute 'getattr' whenever I receive data.