Does CMake support Python3?

Question

I am not able to build a Python wrapper module for my C library via CMake and Swig for Python3. Everything works fine for Python2.x but it looks like CMake cannot find Python3. I already looked around and tried a couple of things.

For example, my python executable links to Python3, as I read CMake will find this version first.

Please see here the SWIG part of the CMakeLists.txt:

FIND_PACKAGE(SWIG REQUIRED)
INCLUDE(${SWIG_USE_FILE})

FIND_PACKAGE(PythonInterp 3)
FIND_PACKAGE(PythonLibs 3)

FIND_PATH(PYTHON_INCLUDE_PATH Python.h
  /usr/include
  /usr/local/include)
INCLUDE_DIRECTORIES(${PYTHON_INCLUDE_DIRS})

INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})

SET(CMAKE_SWIG_FLAGS "")

SET_SOURCE_FILES_PROPERTIES(kissCT3.i PROPERTIES CPLUSPLUS ON)
#SET_SOURCE_FILES_PROPERTIES(kissCT3.i PROPERTIES SWIG_FLAGS "-includeall -py3")

SWIG_ADD_MODULE(kissCT3 python kissCT3.i)
SWIG_LINK_LIBRARIES(kissCT3 libct2d matio kissfft ${PYTHON_LIBRARIES})

Unfortunately, the output after calling cmake shows that only python2.7 is found:

-- Found SWIG: /usr/bin/swig2.0 (found version "2.0.4")
-- Found PythonInterp: /usr/bin/python2.7 (Required is at least version "3")
-- Found PythonLibs: /usr/lib/libpython2.7.so (Required is at least version "3")
-- Configuring done
-- Generating done

Answer 1

Can you make sure your build directory is clean? I had the exact same issue and after cleaning the dir it worked.

Answer 2

CMake 3.12 should help you with your issue. Citing the release notes:

New “FindPython3” and “FindPython2” modules, as well as a new “FindPython” module, have been added to provide a new way to locate python environments.