def delete(self):
        """
        Delete task (does not influence its corresponding directory)

        :return: whether deletion is successful
        :raise: :class:`.TaskError` if the task is already deleted
        """
        if not self._deleted:
            if self.api._req_lixian_task_del(self):
                self._deleted = True
                return True
        raise TaskError('This task is already deleted.')