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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 get_sensor(self, sensor_name):
 """Fetch the sensor with the given name. Parameters sensor_name : str Name of the sensor to retrieve. Returns ------- sensor : Sensor object The sensor with the given name. """

        sensor = self._sensors.get(sensor_name, None)
        if not sensor:
            raise ValueError("Unknown sensor '%s'." % (sensor_name,))
        return sensor