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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 request_sensor_sampling_clear(self, req):
 """Set all sampling strategies for this client to none. Returns ------- success : {'ok', 'fail'} Whether sending the list of devices succeeded. Examples -------- ?sensor-sampling-clear !sensor-sampling-clear ok """

        f = Future()
        @gen.coroutine
        def _clear_strategies():
            self.clear_strategies(req.client_connection)
            raise gen.Return(('ok',))

        self.ioloop.add_callback(lambda: chain_future(_clear_strategies(), f))
        return f