def on_error(self, task_result):
        # TODO should emit a signal
        print('ERROR!!!')
        self.task_exc_type = task_result.exc_type
        self.task_exc = task_result.exc_value
        self.task_exc_stack = traceback.extract_tb(task_result.stack)
        traceback.print_tb(task_result.stack)
        print(task_result)