报这个错是因为没有安装Polygon，大家的第一反应是执行

pip install Polygon

很遗憾，这样做不对！依然显示No module named 'Polygon’的错误。

 File "D:\cv\DBNet.pytorch-master\tools\train.py", line 71, in <module>
    from utils import parse_config
  File "D:\cv\DBNet.pytorch-master\utils\__init__.py", line 7, in <module>
    from .cal_recall.script import  cal_recall_precison_f1
  File "D:\cv\DBNet.pytorch-master\utils\cal_recall\__init__.py", line 4, in <module>
    from .script import  cal_recall_precison_f1
  File "D:\cv\DBNet.pytorch-master\utils\cal_recall\script.py", line 5, in <module>
    import Polygon as plg
ModuleNotFoundError: No module named 'Polygon'

那应该如何解决呢？
如果使用pip install Polygon安装了Polygon，先卸载。

pip uninstall Polygon 
#或者
pip uninstall Polygon3 

然后执行

pip install Polygon3 -i https://pypi.tuna.tsinghua.edu.cn/simple

即可解决。