title: How Use lambda in kivy bind python?
body: <p>I am learning to use the dropdown object with the documentation example</p>
  
  <pre><code>from kivy.uix.dropdown import DropDown
  from kivy.uix.button import Button
  from kivy.base import runTouchApp
  
  dropdown = DropDown()
  for index in range(10):
      btn = Button(text='Value %d' % index, size_hint_y=None, height=44)
  
      btn.bind(on_release=lambda btn: dropdown.select(btn.text))
  
      dropdown.add_widget(btn)
  mainbutton = Button(text='Hello', size_hint=(None, None))
  mainbutton.bind(on_release=dropdown.open)
  
  dropdown.bind(on_select=lambda instance, x: setattr(mainbutton, 'text', x))
  runTouchApp(mainbutton)
  </code></pre>
  
  <p>I know what it is a lambda function, the name of its arguments is supposed to be arbitrary as in a normal function, but in the first case the argument "btn" refers to the Button instance where it is being declared (in order to extract the text from there).</p>
  
  <p>The second occurrence of lambda seems to me even more rare because it has two arguments "instance" and "X" but for the setattr only the "X" is used, I managed to print that argument and it is a </p>