title: Adding modules from opencv_contrib to OpenCV
body: <p>I'm trying to add the <code>xfeatures2d</code> module from <code>opencv_contrib</code> to an existing OpenCV/Python project.</p>
  
  <p>I've downloaded the latest version of the module from <a href="https://github.com/itseez/opencv_contrib" rel="noreferrer">the repo</a>, and built OpenCV again with the following additional params:</p>
  
  <pre><code>OPENCV_EXTRA_MODULES_PATH=/path/to/opencv_contrib-master/modules
  BUILD_opencv_xfeatures2d=ON
  </code></pre>
  
  <p>Excerpt from build log:</p>
  
  <pre><code>-- Installing: /usr/local/lib/python2.7/site-packages/cv2.so
  -- Installing: /usr/local/lib/python3.4/site-packages/cv2.so
  -- Installing: /usr/local/lib/libopencv_xfeatures2d.3.0.0.dylib
  </code></pre>
  
  <p>It appears the new module is installed correctly. I'm able to import <code>cv2</code> in both Python versions. However neither recognise the new features the module is supposed to add.</p>
  
  <pre><code>&gt;&gt;&gt; cv2.SURF()
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  AttributeError: 'module' object has no attribute 'SURF'
  &gt;&gt;&gt; cv2.xfeatures2d.SURF()
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
  AttributeError: 'module' object has no attribute 'xfeatures2d'
  </code></pre>