Call the weight file of yolov3 with OpenCV to obtain the names of the three scale output layers and report an error

ln = [ln[i[0] - 1] for i in net.getUnconnectedOutLayers()]

Error reporting
indexerror: invalid index to scalar variable

This code was a few years ago. It may be a problem with the version. Now it will report an error

Solution:
Remove [0] and modify as below:

ln = [ln[i - 1] for i in net.getUnconnectedOutLayers()]