python 3.6 compile error

[dbermond]

After the update to Python 3.6 I'm getting the following compile error in git master version:

[ 98%] Building CXX object modules/python3/CMakeFiles/opencv_python3.dir/__/src2/cv2.cpp.o
[ 98%] Building CXX object modules/python2/CMakeFiles/opencv_python2.dir/__/src2/cv2.cpp.o
/home/user/abs/opencv-noffmpeg-git/src/opencv-noffmpeg-git/modules/python/src2/cv2.cpp:6:20: fatal error: Python.h: No such file or directory
 #include <Python.h>
                    ^
compilation terminated.
make[2]: *** [modules/python3/CMakeFiles/opencv_python3.dir/build.make:180: modules/python3/CMakeFiles/opencv_python3.dir/__/src2/cv2.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:2063: modules/python3/CMakeFiles/opencv_python3.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[ 99%] Linking CXX shared module ../../lib/cv2.so
[ 99%] Built target opencv_python2
make: *** [Makefile:161: all] Error 2

System information (version)

• OpenCV: git master
• Operating System / Platform: Arch Linux x86_64
• Compiler: gcc 6.2.1
• Python: 3.6.0

Steps to reproduce

cmake \
	-DBUILD_SHARED_LIBS:BOOL=ON \
	\
	-DBUILD_opencv_apps:BOOL=ON             -DBUILD_opencv_calib3d:BOOL=ON  	-DBUILD_opencv_core:BOOL=ON \
	-DBUILD_opencv_features2d:BOOL=ON       -DBUILD_opencv_flann:BOOL=ON    	-DBUILD_opencv_highgui:BOOL=ON \
	-DBUILD_opencv_imgcodecs:BOOL=ON        -DBUILD_opencv_imgproc:BOOL=ON  	-DBUILD_opencv_ml:BOOL=ON \
	-DBUILD_opencv_objdetect:BOOL=ON        -DBUILD_opencv_photo:BOOL=ON    	-DBUILD_opencv_shape:BOOL=ON \
	-DBUILD_opencv_stitching:BOOL=ON        -DBUILD_opencv_superres:BOOL=ON 	-DBUILD_opencv_ts:BOOL=ON \
	-DBUILD_opencv_video:BOOL=ON            -DBUILD_opencv_videoio:BOOL=ON          -DBUILD_opencv_videostab:BOOL=ON \
	-DBUILD_opencv_world:BOOL=OFF \
	\
	-DBUILD_opencv_cudaarithm:BOOL=OFF      -DBUILD_opencv_cudabgsegm:BOOL=OFF      -DBUILD_opencv_cudacodec:BOOL=OFF \
	-DBUILD_opencv_cudafeatures2d:BOOL=OFF  -DBUILD_opencv_cudafilters:BOOL=OFF     -DBUILD_opencv_cudaimgproc:BOOL=OFF \
	-DBUILD_opencv_cudalegacy:BOOL=OFF      -DBUILD_opencv_cudaobjdetect:BOOL=OFF   -DBUILD_opencv_cudaoptflow:BOOL=OFF \
	-DBUILD_opencv_cudastereo:BOOL=OFF      -DBUILD_opencv_cudawarping:BOOL=OFF     -DBUILD_opencv_cudev:BOOL=OFF \
	\
	-DCUDA_64_BIT_DEVICE_CODE:BOOL=OFF \
	-DCUDA_FAST_MATH:BOOL=OFF \
	\
	-DCMAKE_BUILD_TYPE:STRING=Release \
	-DCMAKE_COLOR_MAKEFILE:BOOL=ON \
	-DCMAKE_CXX_FLAGS:STRING="-march=native -O2 -pipe -fstack-protector-strong" \
	-DCMAKE_C_FLAGS:STRING="-march=native -O2 -pipe -fstack-protector-strong" \
	-DCMAKE_INSTALL_PREFIX:PATH=/usr \
	-DCPACK_BINARY_DEB:BOOL=OFF \
	\
	-DPYTHON2_NUMPY_INCLUDE_DIRS:PATH=/usr/include/python2.7/numpy \
	-DPYTHON3_NUMPY_INCLUDE_DIRS:PATH=/usr/include/python3.6m/numpy \
	\
	-DENABLE_FAST_MATH:BOOL=ON \
	\
	-DENABLE_AVX:BOOL=ON     -DENABLE_AVX2:BOOL=ON    -DENABLE_FMA3:BOOL=ON   -DENABLE_POPCNT:BOOL=ON \
	-DENABLE_SSE:BOOL=ON     -DENABLE_SSE2:BOOL=ON    -DENABLE_SSE3:BOOL=ON   -DENABLE_SSSE3:BOOL=ON \
	-DENABLE_SSE41:BOOL=ON   -DENABLE_SSE42:BOOL=ON \
	\
	-DBUILD_EXAMPLES:BOOL=OFF \
	-DBUILD_PERF_TESTS:BOOL=OFF \
	-DBUILD_TESTS:BOOL=OFF \
	-DINSTALL_C_EXAMPLES:BOOL=OFF \
	-DINSTALL_PYTHON_EXAMPLES:BOOL=OFF \
	-DINSTALL_TESTS:BOOL=OFF \
	\
	-DWITH_1394:BOOL=ON       -DWITH_CLP:BOOL=OFF            -DWITH_CUBLAS:BOOL=OFF        -DWITH_CUDA:BOOL=OFF \
	-DWITH_CUFFT:BOOL=OFF     -DWITH_EIGEN:BOOL=ON           -DWITH_FFMPEG:BOOL=OFF        -DWITH_GDAL:BOOL=OFF \
	-DWITH_GIGEAPI:BOOL=OFF   -DWITH_GPHOTO2:BOOL=ON         -DWITH_GSTREAMER:BOOL=ON      -DWITH_GSTREAMER_0_10:BOOL=OFF \
	-DWITH_GTK:BOOL=ON        -DWITH_GTK_2_X:BOOL=ON         -DWITH_IPP_A:BOOL=ON          -DWITH_IPP:BOOL=ON \
	-DWITH_JASPER:BOOL=ON     -DWITH_JPEG:BOOL=ON            -DWITH_LIBV4L:BOOL=ON         -DWITH_NVCUVID:BOOL=ON \
	-DWITH_OPENCL:BOOL=ON     -DWITH_OPENCLAMDBLAS:BOOL=ON   -DWITH_OPENCLAMDFFT:BOOL=ON   -DWITH_OPENCL_SVM:BOOL=ON \
	-DWITH_OPENEXR:BOOL=ON    -DWITH_OPENGL:BOOL=ON          -DWITH_OPENMP:BOOL=ON         -DWITH_OPENNI:BOOL=OFF \
	-DWITH_OPENNI2:BOOL=OFF   -DWITH_PNG:BOOL=ON             -DWITH_PVAPI:BOOL=OFF         -DWITH_QT:BOOL=OFF \
	-DWITH_TBB:BOOL=ON        -DWITH_TIFF:BOOL=ON            -DWITH_UNICAP:BOOL=OFF        -DWITH_V4L:BOOL=ON \
	-DWITH_VTK:BOOL=OFF       -DWITH_WEBP:BOOL=ON            -DWITH_XIMEA:BOOL=OFF         -DWITH_XINE:BOOL=OFF \
	-DWITH_MATLAB:BOOL=OFF    -DWITH_OPENCLAMDFFT:BOOL=ON    -DWITH_PTHREADS_PF:BOOL=ON    -DWITH_VA_INTEL:BOOL=ON \
	\
	-DBUILD_JASPER:BOOL=OFF   -DBUILD_JPEG:BOOL=OFF          -DBUILD_OPENEXR:BOOL=OFF      -DBUILD_PNG:BOOL=OFF \
	-DBUILD_TIFF:BOOL=OFF     -DBUILD_ZLIB:BOOL=OFF \
	\
	-DOPENCV_WARNINGS_ARE_ERRORS:BOOL=OFF \
	-Wno-dev \
	.
	
	make

[alalek]

More details are required:

• CMake stdout (from clean build)
• files from build folder: CMakeCache.txt and CMakeVars.txt (as attachment or use "grep" for related problem keyword)
• failed command line via make VERBOSE=1 (without any -j option)

[dbermond]

Your answer gave me a hint to the solution.

I deleted CMakeCache.txt and CMakeVars.txt and compilation worked as usual.

CMake was not updating python from 3.5 to 3.6, even when explicitly adding all python3 flags pointed to 3.6. Deleting these files allowed CMake to detect python 3.6.

Solved.
Thank you for your assistance.