How to use the dense sampling detector to image with OpenCV3_python?

edit

Thank you for answering. "the Dense was removed..." It is sad. I understand I have to create my own detector. But I don't know how add the keypoints properties to my own detector like a list, list = [(5,5),(10,10),...] Please tell me how. Or, I have to create in xfeatures2d.hpp before make cv2.so files?

Fixed my code to "sift.detectAndCompute()",thank you!

if you want to use your own keypoints, the list should look like:

[
    cv2.KeyPoint(x1,y1,radius),
    cv2.KeyPoint(x2,y2,radius),
    ...
]

(then, ofc, use sift.compute() with that ! :)

The problem was solved with your help. I'm so glad!
Thank you very much!