解决调用surf = cv2.xfeatures2d.SURF_create()报错：cv2.error: OpenCV(4.10.0) D:\a\opencv-python\opencv-pytho

在进行编写特征提取的代码中，使用SURF和SIFT算法一直报错。

# 写法1
sift = cv2.xfeatures2d.SIFT_create()
surf = cv2.xfeatures2d.SURF_create()
# 写法2
sift = cv2.SIFT_create()
surf = cv2.SURF_create()

第一种报错AttributeError: module ‘cv2’ has no attribute ‘xfeatures2d’

第二种报错AttributeError: module ‘cv2’ has no attribute ‘SURF_create’

这两种写法全部会报错，opencv-contrib-python，pip install opencv-contrib-python也去全部安装了，后面发现是在OpenCV 4.0及之后的版本中，SURF和SIFT等专利算法被移至cv2.xfeatures2d模块，并且需要额外的配置才能使用。而我的opencv为4.10的。

cv2.error: OpenCV(4.10.0) D:\a\opencv-python\opencv-python\opencv_contrib\modules\xfeatures2d\src\surf.cpp:1028: error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'cv::xfeatures2d::SURF::create'

解决方法

我的虚拟环境的python是3.7的，直接卸载之前安装的opencv的版本，安装对应版本的opancv

# 卸载之前的OpenCV 
pip uninstall opencv-python
# 安装指定版本的OpenCV和pencv-contrib-python
pip install opencv-python==3.4.2.16
pip install opencv-contrib-python==3.4.2.16

然后我都就可以正常运行，大家一定要注意python的版本不能太高，不然还是会报错，为了避免经常报错，一般我创建虚拟环境时都会指定python=3.7