mmdetection Error when running voc.py: KeyError: ‘NumClassCheckHook is already registered in hook‘

This error is usually caused by the version of mmcv
just click in one by one according to the following error prompt to find utils.py file:
change the code in the circle below:

add in brackets:

finally, it can run successfully.


Similar questions:
keyerror: ‘XXX is already registered in xxx’


Results: it runs perfectly


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