title: AttributeError: 'module' object has no attribute 'xfeatures2d'?
body: <p>I want to use the sift function in open cv, when I do:</p>
  
  <pre><code>cv2.xfeatures2d
  </code></pre>
  
  <p>I get:</p>
  
  <pre><code>AttributeError: 'module' object has no attribute 'xfeatures2d'
  </code></pre>
  
  <p>even <code>cv2.SIFT()</code> does not work. However this seems to work:</p>
  
  <pre><code>cv2.orb_create()
  </code></pre>
  
  <p>I am on open cv 3.3.0, using opencv-contrib-python. I tried using opencv-python but that also gave me same errors.</p>
  
  <p>I tried uninstalling and reinstsalling as well using pip. I am on osx.</p>