title: updating label text in kivy on load
body: <p>I'm brand new to kivy, and trying to build small OSD for my raspberry.</p>
  
  <p>My .kv file looks like this:</p>
  
  <pre><code>BoxLayout:
      orientation: 'vertical'
      Label:
          text_size: self.size
          text: 'OSD'
          font_size: 50
          bold: True
          halign: 'center'
          valign: 'top'
          size_hint: 1, .3
      GridLayout:
          cols: 2
          Label:
              text_size: self.size
              text: 'Total entries in DB: '
              font_size: 30
              bold: False
              halign:  'left'
              size_hint: 1, .1
          Label:
              id: total_db
              text_size: self.size
              text: '366 000 '
              font_size: 30
              bold: True
              color: 0, 1, 0, 1
              halign:  'center'
              size_hint: 1, .1
          Label:
              text_size: self.size
              text: 'Info 1: '
              font_size: 30
              bold: False
              halign: 'left'
              size_hint: 1, .1
          Label:
              id: marked_update
              text_size: self.size
              text: '1328 '
              color: 1, 0, 0, 1
              font_size: 30
              bold: True
              halign:  'center'
              size_hint: 1, .1
      Label:
          text_size: self.size
          text: 'Activity'
          font_size: 50
          bold: True
          halign: 'center'
          valign: 'top'
          size_hint: 1, .3
      Label:
          text: ''
          font_size: 10
          halign: 'center'
          valign: 'top'
          size_hint: 1, .08
  
      GridLayout:
          cols: 4
          Button:
              text: 'DS 01'
              font_size: 25
              background_color: 1, 0, 0, 1
          Button:
              text: 'DS 02'
              font_size: 25
              background_color: 0, 1, 0, 1
          Button:
              text: 'DS 03'
              font_size: 25
              background_color: 0, 1, 0, 1
          Button:
              text: 'DS 04'
              font_size: 25
              background_color: 0, 1, 0, 1
  </code></pre>
  
  <p>This produce the look I want. I wan to periodically update the two labels texts with IDs with values I extract later on... but I can't even update them from python which looks like this:</p>
  
  <pre><code>import kivy
  kivy.require('1.10.1')
  
  from kivy.app import App
  from kivy.uix.boxlayout import BoxLayout
  from kivy.uix.label import Label
  from kivy.clock import Clock
  
  class BoxLayout(BoxLayout):
      def __init__(self, **kwargs):
          super(BoxLayout, self).__init__(**kwargs)
          Clock.schedule_once(self.update_txt, 0)
  
      def update_txt(self, *args):
          self.label.ids.marked_update.txt='updated from python'
  
  class osdApp(App):
      def build(self):
          self.title = 'OSD'
          return BoxLayout()
  
  
  if __name__ == '__main__':
      osdApp().run()
  </code></pre>
  
  <p>I was thinking to start clock that calls the update_txt function and that could change the value, but I keep getting error that ids does not exists... and so on, I'm bread new to object oriented programming and I can't figure this simple thing out</p>