def sensor_id(self):
        """The id of the sensor of this data point.

        Returns:

            The id of the sensor that generated this datapoint. Will
            throw an AttributeError if no sensor id was found in the
            underlyign data.

        """
        if hasattr(self, '_sensor_id'):
            return self._sensor_id
        relationships = self._json_data.get('relationships')
        sensor_id = relationships.get('sensor').get('data').get('id')
        self._sensor_id = sensor_id
        return sensor_id