How to use the tasklib.backends.TaskWarriorException function in tasklib

args, config_override=config_override)
        logger.debug(u' '.join(command_args))

        env = os.environ.copy()
        if self.taskrc_location:
            env['TASKRC'] = self.taskrc_location
        p = subprocess.Popen(command_args, stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE, env=env)
        stdout, stderr = [x.decode('utf-8') for x in p.communicate()]
        if p.returncode and allow_failure:
            if stderr.strip():
                error_msg = stderr.strip()
            else:
                error_msg = stdout.strip()
            error_msg += u'\nCommand used: ' + u' '.join(command_args)
            raise TaskWarriorException(error_msg)

        # Return all whole triplet only if explicitly asked for
        if not return_all:
            return stdout.rstrip().split('\n')
        else:
            return (stdout.rstrip().split('\n'),
                    stderr.rstrip().split('\n'),
                    p.returncode)

"""Save a task into TaskWarrior database using add/modify call"""

        args = [task['uuid'], 'modify'] if task.saved else ['add']
        args.extend(self._get_modified_task_fields_as_args(task))
        output = self.execute_command(args)

        # Parse out the new ID, if the task is being added for the first time
        if not task.saved:
            id_lines = [l for l in output if l.startswith('Created task ')]

            # Complain loudly if it seems that more tasks were created
            # Should not happen.
            # Expected output: Created task 1.
            #                  Created task 1 (recurrence template).
            if len(id_lines) != 1 or len(id_lines[0].split(' ')) not in (3, 5):
                raise TaskWarriorException(
                    'Unexpected output when creating '
                    'task: %s' % '\n'.join(id_lines),
                )

            # Circumvent the ID storage, since ID is considered read-only
            identifier = id_lines[0].split(' ')[2].rstrip('.')

            # Identifier can be either ID or UUID for completed tasks
            try:
                task._data['id'] = int(identifier)
            except ValueError:
                task._data['uuid'] = identifier

        # Refreshing is very important here, as not only modification time
        # is updated, but arbitrary attribute may have changed due hooks
        # altering the data before saving

# Make a copy, removing ID and UUID. It's most likely invalid
            # (ID 0) if it failed to match a unique task.
            data = copy.deepcopy(task._data)
            data.pop('id', None)
            data.pop('uuid', None)

            taskfilter = self.filter_class(self)
            for key, value in data.items():
                taskfilter.add_filter_param(key, value)

            output = self.execute_command(['export'] +
                                          taskfilter.get_filter_params())

        # If more than 1 task has been matched still, raise an exception
        if not valid(output):
            raise TaskWarriorException(
                'Unique identifiers {0} with description: {1} matches '
                'multiple tasks: {2}'.format(
                    task['uuid'] or task['id'], task['description'], output)
            )

        return json.loads(output[0])

def filter_tasks(self, filter_obj):
        self.enforce_recurrence()
        args = ['export'] + filter_obj.get_filter_params()
        tasks = []
        for line in self.execute_command(args):
            if line:
                data = line.strip(',')
                try:
                    filtered_task = Task(self)
                    filtered_task._load_data(json.loads(data))
                    tasks.append(filtered_task)
                except ValueError:
                    raise TaskWarriorException('Invalid JSON: %s' % data)
        return tasks