[Python] Cannot install openCV 3.1.0 with python3. CMAKE not including or linking python...

I'm trying to get OpenCV 3.1.0 installed with Python3 on my machine. Because I have Ubuntu 16.04, I am following this guide exactly:

http://www.pyimagesearch.com/2016/10/24/ubuntu-16-04-how-to-install-opencv/

However, I have trouble in step 4, after running cmake. The output of my cmake program has this snippet:

-- OpenCL:
-- Version: dynamic
-- Include path: /home/kevin/opencv-3.1.0/3rdparty/include/opencl/1.2
-- Use AMDFFT: NO
-- Use AMDBLAS: NO
--
-- Python 2:
-- Interpreter: /home/kevin/.virtualenvs/cv/bin/python (ver 3.5.2)
--
-- Python 3:
-- Interpreter: /home/kevin/.virtualenvs/cv/bin/python3 (ver 3.5.2)
--
-- Python (for build): /home/kevin/.virtualenvs/cv/bin/python
--
-- Java:
-- ant: NO
-- JNI: /usr/lib/jvm/java-8-oracle/include /usr/lib/jvm/java-8-oracle/include/linux /usr/lib/jvm/java-8-oracle/include
-- Java wrappers: NO
-- Java tests: NO


The cmake file doesnt seem to properly link the missing properties under the python section (libraries, numpy, packages_path). I tried compiling opencv and installing it, and when I load python3 and import cv, it says it could not find the cv package.

I tried modifying the CMAKE command, so instead of using what the guide suggested, I added three parameters to force cmake to include the missing python properties (the last three properties were my modification):

cmake -D CMAKE_BUILD_TYPE=RELEASE \
-D CMAKE_INSTALL_PREFIX=/usr/local \
-D INSTALL_PYTHON_EXAMPLES=ON \
-D INSTALL_C_EXAMPLES=OFF \
-D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib-3.1.0/modules \
-D PYTHON_EXECUTABLE=~/.virtualenvs/cv/bin/python \
-D BUILD_EXAMPLES=ON \
-D PYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so \
-D PYTHON_NUMPY_INCLUDE_DIR=~/.virtualenvs/cv/lib/python3.5/site-packages/numpy/core/include \
-D PYTHON_PACKAGES_PATH=~/.virtualenvs/cv/lib/python3.5/site-packes ..


But still, the output of cmake is the same (it only lists the interpretter, and no other python properties), and when I try building opencv and installing it, my python interpretter could not find the opencv package.

My /usr/local/lib/python3.5/ file did NOT have a site-packages directory after I finished installing opencv either.

Can anyone point me in the right direction? I've been trying to search the past few hours on how to fix this, but could not find a way so far, so I'd greatly appreciate any guidance. Thank you!

Update

I realize that I have to add -D BUILD_opencv_python3=yes to the cmake command so that opencv looks for the python libraries. However, this is the new output that I get from cmake:

-- Python 3:
-- Interpreter: /home/kevin/.virtualenvs/cv/bin/python (ver 3.5.2)
-- Libraries: NO
-- numpy: NO (Python3 wrappers can not be generated)
-- packages path: lib/python3.5/site-packages


Any idea why cmake is not finding my python 3 libraries correctly (even when I add "-D PYTHON_LIBRARY=/usr/lib/x86_64-linux-gnu/libpython3.5m.so " to the cmake options)?

Update

I fixed the problem by deleting the entire /build directory, and running cmake on a fresh directory. I think the error continued to show up because of some caching done by cmake, but adding the flag -D BUILD_opencv_python3=yes seem to do the trick for me.

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