【pytorch踩坑記錄】NameError: name ‘opt’ is not defined

學習陳雲老師的《深度學習框架PyTorch:入門與實踐 》貓狗二分類實戰時遇到的問題。
運行環境：
問題描述：

(pytorch) D:\SoftWares-Academic\python_workspace\pytorch-best-practice>python main.py help

    usage : python file.py <function> [--args=value]
    <function> := train | test | help
    example:
            python main.py train --env='env0701' --lr=0.01
            python main.py test --dataset='path/to/dataset/root/'
            python main.py help
    avaiable args:
Traceback (most recent call last):
  File "main.py", line 171, in <module>
    import fire
  File "D:\SoftWares-Academic\Anaconda3\envs\pytorch\lib\site-packages\fire\core.py", line 138, in Fire
    component_trace = _Fire(component, args, parsed_flag_args, context, name)
  File "D:\SoftWares-Academic\Anaconda3\envs\pytorch\lib\site-packages\fire\core.py", line 468, in _Fire
    target=component.__name__)
  File "D:\SoftWares-Academic\Anaconda3\envs\pytorch\lib\site-packages\fire\core.py", line 672, in _CallAndUpdateTrace
    component = fn(*varargs, **kwargs)
  File "main.py", line 166, in help
    from inspect import getsource
NameError: name 'opt' is not defined

很迷的錯誤，跟書附帶的代碼一樣的。在main.py函數頭部已經添加了from config import opt，但是還報錯NameError: name ‘opt’ is not defined。
最後，在調用的方法help裏直接添加from config import opt，沒有錯誤了，但不知道原理。