How to use the tasklib.raise_exception function in tasklib

def on_completed(_):
            self.status = "successfully completed"
            self._localization_storage.save_pldata_to_disk()
            logger.info("camera localization completed")
            self.on_localization_ended()

        def on_canceled_or_killed():
            self._localization_storage.save_pldata_to_disk()
            logger.info("camera localization canceled")
            self.on_localization_ended()

        self._task = self._create_task()
        self._task.add_observer("on_yield", on_yield)
        self._task.add_observer("on_completed", on_completed)
        self._task.add_observer("on_canceled_or_killed", on_canceled_or_killed)
        self._task.add_observer("on_exception", tasklib.raise_exception)
        self._task.add_observer("on_started", self.on_localization_started)
        logger.info("Start camera localization")
        self.status = "0% completed"

def validate_gaze_mapper(self, gaze_mapper):
        def validation_completed(accuracy_and_precision):
            accuracy, precision = accuracy_and_precision
            gaze_mapper.accuracy_result = "{:.1f}° from {} / {} samples".format(
                accuracy.result, accuracy.num_used, accuracy.num_total
            )
            gaze_mapper.precision_result = "{:.1f}° from {} / {} samples".format(
                precision.result, precision.num_used, precision.num_total
            )

        task = worker.validate_gaze.create_bg_task(
            gaze_mapper, self._reference_location_storage
        )
        task.add_observer("on_completed", validation_completed)
        task.add_observer("on_exception", tasklib.raise_exception)
        self._task_manager.add_task(task)

def calculate(self, calibration):
        def on_calibration_completed(status_and_result):
            calibration.status, calibration.result = status_and_result
            self._calibration_storage.save_to_disk()
            self.on_calibration_computed(calibration)

        task = worker.create_calibration.create_task(
            calibration, all_reference_locations=self._reference_location_storage
        )
        task.add_observer("on_completed", on_calibration_completed)
        task.add_observer("on_exception", tasklib.raise_exception)
        self._task_manager.add_task(task)
        return task

def on_completed(_):
            self._detection_storage.save_pldata_to_disk()
            logger.info("marker detection completed")
            self.on_detection_ended()

        def on_canceled_or_killed():
            self._detection_storage.save_pldata_to_disk()
            logger.info("marker detection canceled")
            self.on_detection_ended()

        self._task = self._create_task()
        self._task.add_observer("on_yield", on_yield)
        self._task.add_observer("on_completed", on_completed)
        self._task.add_observer("on_canceled_or_killed", on_canceled_or_killed)
        self._task.add_observer("on_exception", tasklib.raise_exception)
        self._task.add_observer("on_started", self.on_detection_started)
        logger.info("Start marker detection")

def start_detection(self):
        def on_detection_yields(detection):
            self._reference_location_storage.add(detection)

        def on_detection_completed(_):
            self._reference_location_storage.save_to_disk()

        self._detection_task = worker.detect_circle_markers.CircleMarkerDetectionTask()
        self._detection_task.add_observer("on_exception", tasklib.raise_exception)
        self._detection_task.add_observer(
            "on_started", lambda: self.on_detection_started(self._detection_task)
        )
        self._detection_task.add_observer("on_yield", on_detection_yields)
        self._detection_task.add_observer("on_completed", on_detection_completed)
        self._task_manager.add_task(self._detection_task)
        return self._detection_task

reason = (
                        "not enough markers with the defined origin marker id "
                        "were collected"
                    )
                else:
                    reason = "not enough markers were collected"

                self.status = "failed: " + reason
            logger.info("markers 3d model optimization '{}' ".format(self.status))

            self._optimization_storage.save_plmodel_to_disk()

        self._task = self._create_task()
        self._task.add_observer("on_yield", on_yield)
        self._task.add_observer("on_completed", on_completed)
        self._task.add_observer("on_exception", tasklib.raise_exception)
        self._task.add_observer("on_started", self.on_optimization_started)
        logger.info("Start markers 3d model optimization")
        self.status = "0% completed"