new_contents: from kivy.lang import Builder
  from kivy.app import App
  from kivy.uix.boxlayout import BoxLayout
  
  Builder.load_string('''
  [BlehItem@BoxLayout]:
      orientation: 'vertical'
      Label:
          text: str(ctx.idx)
      Button:
          text: ctx.word
  ''')
  
  
  class BlehApp(App):
  
      def build(self):
          root = BoxLayout()
          for idx, word in enumerate(('Hello', 'World')):
              wid = Builder.template('BlehItem', {
                  'idx': idx, 'word': word,
              })
              root.add_widget(wid)
          return root
  
  if __name__ == '__main__':
      BlehApp().run()
  
  
subject: add builder_template.py example, to show how the user can create widget from template