def add_udev_trigger(self, trigger_action, subsystem):
        """
        Subscribe to the requested udev subsystem and apply the given action.
        """
        if self._py3_wrapper.udev_monitor.subscribe(self, trigger_action, subsystem):
            if trigger_action == "refresh_and_freeze":
                # FIXME: we may want to disable refresh instead of using cache_timeout
                self.module_class.cache_timeout = Py3.CACHE_FOREVER

        Subscribe to the requested udev subsystem and apply the given action.
        
py3status/module.py