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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 future_check_sensor(self, name, update=None):
 """Check if the sensor exists. Used internally by future_get_sensor. This method is aware of synchronisation in progress and if inspection of the server is allowed. Parameters name : str Name of the sensor to verify. update : bool or None, optional If a katcp request to the server should be made to check if the sensor is on the server now. Notes ----- Ensure that self.state.data_synced == True if yielding to future_check_sensor from a state-change callback, or a deadlock will occur. """

        exist = False
        yield self.until_data_synced()
        if name in self._sensors_index:
            exist = True
        else:
            if update or (update is None and self._update_on_lookup):
                yield self.inspect_sensors(name)
                exist = yield self.future_check_sensor(name, False)

        raise tornado.gen.Return(exist)