How to change text of a label in the kivy language with python

Question

I was wondering how I could change the text of a label made inside the Kivy language using Python. Like how would I have user input from python be made as the text of a label in kivy. (By the way I have the formatting correct in the actual program but I screwed up pasting it to stackoverflow) Say if I wanted to make the text of the label in from the code be a random number generated in python how would I go about doing that?

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.graphics import Color, Rectangle
from kivy.properties import ObjectProperty

# Create both screens. Please note the root.manager.current: this is how
# you can control the ScreenManager from kv. Each screen has by default a
# property manager that gives you the instance of the ScreenManager used.


Builder.load_string("""
<ButImage@ButtonBehavior+AsyncImage>
<TutImage@ButtonBehavior+AsyncImage>
<MenuScreen>:
GridLayout:
    cols: 4
    row_force_default: True
    col_default_width: 175
    row_default_height: 150
    padding: 15
    spacing: 15
    canvas.before:
        BorderImage:
            # BorderImage behaves like the CSS BorderImage
            border: 10, 10, 10, 10
            source: '/Users/clayhigh/Desktop/kivy/aot.png'
            pos: self.pos
            size: self.size
    Button:
        text: 'Goto settings'
        background_color: 1,0,0,0.5
        on_press: root.manager.current = 'settings'
    ButImage:
        on_press: root.manager.current = 'UBW'
        id: but
        size_hint: .5, .5
        opacity: 1 if self.state == 'normal' else .5
        allow_stretch: True
        keep_ratio: False
        source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
        Label:
            center: but.center
            text: "UBW"
            color: 0.78,0.145,0.016,2
    ButImage:
        id: lh
        size_hint: .5, .5
        opacity: 1 if self.state == 'normal' else .5
        allow_stretch: True
        keep_ratio: False
        source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
        Label:
            center: lh.center
            text: "LH 2"
            color: 0,0,0,1
    ButImage:
        id: ttl
        size_hint: .5, .5
        opacity: 1 if self.state == 'normal' else .5
        allow_stretch: True
        keep_ratio: False
        source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
        Label:
            center: ttl.center
            text: "TwTl"
            color: 0,0,0,1
    ButImage:
        id: gris
        size_hint: .5, .5
        opacity: 1 if self.state == 'normal' else .5
        allow_stretch: True
        keep_ratio: False
        source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
        Label:
            center: gris.center
            text: "Gris"
            color: 0,0,0,1
    ButImage:
        id: shig
        size_hint: .5, .5
        opacity: 1 if self.state == 'normal' else .5
        allow_stretch: True
        keep_ratio: False
        source: 'http://s3.amazonaws.com/rapgenius/1361742626_beautiful-ocean-beautiful-pictures-27115524-1440-900.jpg'
        Label:
            center: shig.center
            text: "Shig"
            color: 0,0,0,1
    Button:
        text: 'Test3'
        background_color: 1,0,0,0.5
    Button:
        text: 'Test4'
        background_color: 1,0,0,0.5
    Button:
        text: 'Quit'
        background_color: 1,0,0,0.5
        on_press: App.on_stop

<SettingsScreen>:
GridLayout:
    row_force_default: True
    row_default_height: 100
    cols: 2
    canvas.before:
        BorderImage:
            # BorderImage behaves like the CSS BorderImage
            border: 10, 10, 10, 10
            source: '/Users/clayhigh/Desktop/kivy/ato.jpeg'
            pos: self.pos
            size: self.size
    Button:
        text: 'Button'
        color: 0,0,.5
        background_color: 1,0,0,1
    Button:
        text: 'Back to menu'
        background_color: 1,0,0,1
        on_press: root.manager.current = 'menu'
<UBW>:
GridLayout:
    row_force_default: True
    row_default_height: 100
    cols: 2
    canvas.before:
        Color:
            rgb: .5, .5, .5
        Rectangle:
            pos: self.pos
            size: self.size
        Color:
            rgb: 1, 1, 1
        BorderImage:
            # BorderImage behaves like the CSS BorderImage
            border: 10, 10, 10, 10
            source: '/Users/clayhigh/Desktop/kivy/fsn.jpg'
            pos: self.pos
            size: self.size
    Button:
        text: 'Back to menu'
        color: 0,0,.5
        on_press: root.manager.current = 'menu'
        background_color: 1,0,0,1
    Label:
        id: AName
        text: "F S/N: UBW"
        font_size: '24sp'
""")

# Declare both screens


class MenuScreen(Screen):
pass


class SettingsScreen(Screen):
pass


class UBW(Screen):
pass

# Create the screen manager
sm = ScreenManager()
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))
sm.add_widget(UBW(name='UBW'))


class TestApp(App):

def build(self):
    return sm

if __name__ == '__main__':
TestApp().run()

Answer 1

Text of a label can be a kivy property, which can be later changed and since it is a kivy property it will automatically updated everywhere. Here is an example of your .py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.properties import StringProperty
import random

class YourWidget(Widget):
    random_number = StringProperty()

    def __init__(self, **kwargs):
        super(YourWidget, self).__init__(**kwargs)
        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()

and your .kv

<YourWidget>:
    BoxLayout:
        size: root.size
        Button:
            id: button1
            text: "Change text"
            on_release: root.change_text()
        Label:
            id: label1
            text: root.random_number

When you click the button, it will call change_text() function, which will randomly change the text of the label to random integer between 1 and 100.