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

This is a known bug, but unfortunately it's not resolved in this moment, see http://www.cmake.org/Bug/print_bug_page.php?bug_id=13794

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.

Answer 3

I kind of solved the problem by setting the python version manually. This is not really recommendable but it works for now (note that you have to use your own installation path of the python version you want to use):

SET(PYTHON_INCLUDE_PATH /usr/include/python3.2mu)
SET(PYTHON_LIBRARIES /usr/lib/libpython3.2mu.so)
SET(PYTHON_EXECUTABLE /usr/bin/python3.2mu)
SET(PYTHON_INCLUDE_DIR  /usr/include/python3.2mu)

Answer 4

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