module cv2.cv2 has no attribute xfeatures2d

图像拼接中出现错误：module cv2.cv2 has no attribute xfeatures2d
安装contrib，安装之后出现另一错误：module cv2.cv2 has no attribute SIFT_CREAT。
先卸载然后重新安装
pip uninstall opencv-python
pip uninstall opencv-contrib-python
pip install -i https://pypi.tuna.tsinghua.edu.cn/simple opencv-python3.4.2.16
pip install -i https://pypi.tuna.tsinghua.edu.cn/simple opencv-contrib-python3.4.2.16