code: def force_screen_saver(self, mode, onerror = None):
          
          request.ForceScreenSaver(display = self.display,
                                   onerror = onerror,
                                   mode = mode)
docs: If mode is X.ScreenSaverActive the screen saver is activated.
          If it is X.ScreenSaverReset, the screen saver is deactivated as
          if device input had been received.