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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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