def _selection_scroll(event, params):
 if (event.step < 0):
  _change_channel_group((-1), params)
 elif (event.step > 0):
  _change_channel_group(1, params)

def _selection_scroll ( event , params ) : if ( event . step < 0 ) : _change_channel_group ( ( - 1 ) , params ) elif ( event . step > 0 ) : _change_channel_group ( 1 , params )
callback for scroll in selection dialog .