AttributeError: module ‘cv2‘ has no attribute ‘SIFT‘解决总结

遇到该问题时，网友多是建议补个包，即pip install opencv-contrib-python
我在补完之后又出现下面这样的错误：
OpenCV(3.4.3) C:\projects\opencv-python\opencv_contrib\modules\xfeatures2d\src\sift.cpp:1207: error: (-213:The function/feature is not implemented) This algorithm is patented（专利保护） and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function ‘cv::xfeatures2d::SIFT::create’
将opencv版本退到3.4.2即可解决，卸载之前的包（pip uninstall opencv-python），然后

pip install opencv-python==3.4.2.16
pip install opencv-contrib-python==3.4.2.16

注意以上两条命令==左右没有空格

如果错误：

　　'module' object has no attribute 'xfeatures2d'

原因：opencv将SIFT等算法整合到xfeatures2d集合里面了。

siftDetector=cv2.SIFT()

变更后为

siftDetector= cv2.xfeatures2d.SIFT_create()

参考：AttributeError: module 'cv2' has no attribute 'SIFT'