title: Watching a property for changes
body: <p>I need a function similar to <code>gobject.io_add_watch</code> but for a variable. For example it needs to watch the variable <code>stop</code> initialized to <code>stop = False</code> and when stop is changed to <code>True</code> it must call a function. I can't have a separate thread watching the variable in a loop with a time.sleep.</p>
  
  <p>Is there such a function or a way to do that ?</p>