title: module 'cv2.cv2' has no attribute 'xfeatures2d' (OpenCV 4.1.2)
body: <pre><code>sift  = cv2.xfeatures2d.SIFT_create()             
  
  AttributeError                         Traceback (most recent call last)
  &lt;ipython-input-49-11572687581a&gt; in &lt;module&gt;()
  
        8 gray = cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)
        9 #create sift object
  ---&gt; 10 sift  = cv2.xfeatures2d.SIFT_create()
       11 #calculate keypoints and their orientation
       12 keypoints,descriptors = sift.detectAndCompute(gray,None)
  </code></pre>
  
  <p>AttributeError: module 'cv2.cv2' has no attribute 'xfeatures2d'</p>