title: AttributeError: module 'cv2.cv2' has no attribute 'xfeatures2d' [Opencv 3.4.3]
body: <p>I have opencv 3.4.3 installed (using <code>pip3 install opencv-python</code> and <code>pip3 install opencv-python-contrib</code>) </p>
  
  <p>When I run a code containing this line:<br>
  <code>sift = cv2.xfeatures2d.SIFT_create()</code><br>
  I got this error: </p>
  
  <pre><code>AttributeError: module 'cv2.cv2' has no attribute 'xfeatures2d'
  </code></pre>
  
  <p>Is <code>xfeatures2d</code> function not anymore supported by opencv 3.4.3? </p>