IndexError: list index out of range

[liuqiang1227]

[ERROR] [1703211340.680502]: bad callback: <bound method DetectorManager.imageCb of <main.DetectorManager object at 0x7ff2990bb880>>
Traceback (most recent call last):
File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 750, in _invoke_callback
cb(msg)
File "/home/a/123/src/darknet_ros/yolov3_pytorch_ros/src/detector.py", line 138, in imageCb
detection_msg.Class = self.classes[int(det_class)]
IndexError: list index out of range