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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 start(self):
 """ Start standing by. A periodic command like 'current_url' will be sent to the webdriver instance to prevent it from timing out. """

        self._end_time = datetime.now() + timedelta(seconds=self._max_time)
        self._thread = Thread(target=lambda: self.__stand_by_loop())
        self._keep_running = True
        self._thread.start()
        return self