title: Change button text value for on_press event in Kivy
body: <p>My application has a single  button with text value as '2'. I want to change the text value to 100 on <code>on_press</code> event</p>
  
  <p>My attempt:</p>
  
  <pre><code>#!/usr/bin/kivy
  import kivy
  kivy.require('1.7.2')
  
  from random import random
  from random import choice
  from kivy.app import App
  from kivy.lang import Builder
  from kivy.uix.screenmanager import ScreenManager, Screen
  from kivy.uix.gridlayout import GridLayout
  from kivy.uix.button import Button
  
  r1c2=random()
  Builder.load_string("""
  &lt;Highest&gt;:
      r1c2: str(2)
      GridLayout:
          cols: 1
          Button:
              text: root.r1c2
              on_press: root.new()
  """)
  
  class Highest(Screen):
      def new(self):
          r1c2=str(100)
  
  
  # Create the screen manager
  sm = ScreenManager()
  sm.add_widget(Highest(name='Highest'))
  
  class TestApp(App):
  
      def build(self):
          return sm
  
  if __name__ == '__main__':
      TestApp().run()
  </code></pre>
  
  <p>Error: Currently, nothing happens when the button is pressed. Please help</p>