title: make child widget get the input keypress with urwid on python
body: <p>I can make a widget inside another widget, as example an <code>urwid.Frame</code> father could have as <code>body</code> an <code>urwid.Pile</code> widget as child.
  In this situation, the father should process some input keys when the child have to treat some specific others keys.</p>
  <p>Like in this functional example:</p>
  <pre><code>import urwid
  
  
  class NewFrame(urwid.Frame):
      def __init__(self, givenBody):
          super().__init__(urwid.Filler(givenBody, &quot;top&quot;))
  
      def keypress(self, size, key):
          if key  in ('f'):
              print(&quot;We are in NewFrame object&quot;)
  
          return super(NewFrame, self).keypress(size, key)
  
  
  class NewPile(urwid.Pile):
      def __init__(self, givenList):
          super().__init__(givenList)
  
      def keypress(self, size, key):
          if key  in ('p'):
              print(&quot;We are in NewPile object&quot;)
  
          return super(NewPile, self).keypress(size, key)
  
  
  
  master_pile = NewPile([
      urwid.Text(&quot;foo&quot;),
      urwid.Divider(u'─'),
  ])
  
  
  frame = NewFrame(master_pile)
  
  loop = urwid.MainLoop(frame)
  loop.run()
  
  </code></pre>
  <p>When I press <kbd>f</kbd> I could see the <code>Text</code> widget “We are in NewFrame”. But when I press <kbd>p</kbd>, the <code>NewPile</code> text doesn’t appear and nothing happens.</p>
  <p>So, how could I make the child widget get input keys, especially when they are not matched by the <code>.keypress()</code> method of the parent?</p>