raise ImportError("{} doesn't contains class named 'Exp'".format(exp_file)) ImportError: exps/default/nano.py doesn't contains class named 'Exp'

li@li-desktop:~/Desktop/YOLOX-main$ python3 tools/demo.py image -f exps/default/nano.py -c yolox_nano.pth --path assets/dog.jpg --conf 0.25 --nms 0.45 --tsize 640 --save_result --device gpu

Traceback (most recent call last):
File "/home/li/Desktop/YOLOX-main/yolox/exp/build.py", line 13, in get_exp_by_file
current_exp = importlib.import_module(os.path.basename(exp_file).split(".")[0])
File "/usr/lib/python3.6/importlib/init.py", line 126, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "", line 994, in _gcd_import
File "", line 971, in _find_and_load
File "", line 955, in _find_and_load_unlocked
File "", line 665, in _load_unlocked
File "", line 674, in exec_module
File "", line 781, in get_code
File "", line 741, in source_to_code
File "", line 219, in _call_with_frames_removed
File "exps/default/nano.py", line 36
backbone = YOLOPAFPN(self.depth, self.width, in_channels=in_channels, self.act, depthwise=True)
^
SyntaxError: positional argument follows keyword argument

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "tools/demo.py", line 312, in
exp = get_exp(args.exp_file, args.name)
File "/home/li/Desktop/YOLOX-main/yolox/exp/build.py", line 51, in get_exp
return get_exp_by_file(exp_file)
File "/home/li/Desktop/YOLOX-main/yolox/exp/build.py", line 16, in get_exp_by_file
raise ImportError("{} doesn't contains class named 'Exp'".format(exp_file))
ImportError: exps/default/nano.py doesn't contains class named 'Exp'

Start at exps/default/nano.py line 36, where the traceback reports the syntax error while loading the experiment file. Check the YOLOPAFPN call's argument ordering, then rerun the tools/demo.py command from the issue; done means the experiment imports successfully without the misleading ImportError.