Warning Building Opencv 3.0 =>CMake Warning: (...) not used by the project: BUILD_NEW_PYTHON_SUPPORT

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I am running in virtual box - linux mint XFCE 64 bits.

While trying to build opencv, I got the following message in the end of building: -- Configuring done -- Generating done CMake Warning: Manually-specified variables were not used by the project:

BUILD_NEW_PYTHON_SUPPORT

Since I want to use opencv with python bindings, I would like to know if this flag BUILD_NEW_PYTHON_SUPPORT is strictly necessary and why I got this warning.

My steps to build were: References: http://docs.opencv.org/3.0-last-rst/d... http://www.bogotobogo.com/OpenCV/open...

[compiler] sudo apt-get install build-essential
[required] sudo apt-get install cmake git libgtk2.0-dev pkg-config libavcodec-dev libavformat-dev libswscale-dev
[optional] sudo apt-get install python-dev python-numpy libtbb2 libtbb-dev libjpeg-dev libpng-dev libtiff-dev libjasper-dev libdc1394-22-dev


cd ~/<my_working_directory>
git clone https://github.com/Itseez/opencv.git
git clone https://github.com/Itseez/opencv_contrib.git

cd ~/opencv
mkdir build
cd build

[I had to install: sudo apt-get install qt5-default]   

           (java support)            (docs)               (extra - contrib modules)
cmake -DBUILD_SHARED_LIBS=OFF -D BUILD_DOCS=ON -D OPENCV_EXTRA_MODULES_PATH=<path-to-opencv_contrib>/modules -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local -D WITH_TBB=ON -D BUILD_NEW_PYTHON_SUPPORT=ON -D WITH_V4L=ON -D INSTALL_C_EXAMPLES=ON -D INSTALL_PYTHON_EXAMPLES=ON -D BUILD_EXAMPLES=ON -D WITH_QT=ON -D WITH_OPENGL=ON ..

(I changed the path-to-opencv_contrib to the right one)

Thank you for your help.