參考鏈接：
https://stackoverflow.com/questions/18561910/opencv-python-cant-use-surf-sift
For recent information on this issue (as of Sept 2015) consult this page.
Most information on this question here is obsolete.
What pyimagesearch is saying is that SURF/SIFT were moved to opencv_contrib because of patent issues.
For installation there is also a nice page that tells you how to install opencv with opencv_contrib and Python support so you get SURF/SIFT.
Notice that the API also changed. Now it's like this:
sift = cv2.xfeatures2d.SIFT_create()Before I found the above pages, I also suffered quite a bit. But the pages listed do a very good job of helping with installation and explaining what's wrong.