how to get opencv_contrib module in anaconda
The question is old but I thought to update the answer with the latest information. My Anaconda version is 2019.10 and build channel is py_37_0 . I  used pip install opencv-python==3.4.2.17 and pip install opencv-contrib-python==3.4.2.17. Now they are also visible as installed packages in Anaconda navigator and I am able to use patented methods like SIFT etc.
Can anyone tell me commands to get contrib module for anaconda
I need that module for 
 matches = flann.knnMatch(des1,des2,k=2)
to run correctly
error thrown is 
cv2.error: ......\modules\python\src2\cv2.cpp:163: error: (-215) The data should normally be NULL! in function NumpyAllocator::allocate
Also I am using Anaconda openCV version 3, and strictly dont want to switch to lower versions 
P.S. as suggested at many places to edit file cv2.cpp option is not available with anaconda.