No such operator torchvision::nms
When I try to run yoloV3 detect,it happend the error 

op = torch._C._jit_get_operation(qualified_op_name)

RuntimeError: No such operator torchvision::nms


Though this code is the source code of torchvision ,I try sevaral time to correct the code by the tips  with failure.

I had the same problem on Ubuntu 18.04. Upgrading python to 3.8 and Installing fresh torch and torchvision libraries worked for me.
virtualenv -p python3.8 torch17
source torch17/bin/activate
pip install cython matplotlib tqdm scipy ipython ninja yacs opencv-python ffmpeg opencv-contrib-python Pillow scikit-image scikit-learn lmfit imutils pyyaml jupyterlab==3
pip install torch==1.7.1+cu101 torchvision==0.8.2+cu101 torchaudio==0.7.2 -f https://download.pytorch.org/whl/torch_stable.html

I tried the solutions discussed in some pytorch forums and github but that did not help.
