upm/cmake/modules/OpenCVDetectPython.cmake

# Find specified Python version
# Arguments:
#   preferred_version (value): Version to check for first
#   min_version (value): Minimum supported version
#   library_env (value): Name of Python library ENV variable to check
#   include_dir_env (value): Name of Python include directory ENV variable to check
#   found (variable): Set if interpreter found
#   executable (variable): Output of executable found
#   version_string (variable): Output of found version
#   version_major (variable): Output of found major version
#   version_minor (variable): Output of found minor version
#   libs_found (variable): Set if libs found
#   libs_version_string (variable): Output of found libs version
#   libraries (variable): Output of found Python libraries
#   library (variable): Output of found Python library
#   debug_libraries (variable): Output of found Python debug libraries
#   debug_library (variable): Output of found Python debug library
#   include_path (variable): Output of found Python include path
#   include_dir (variable): Output of found Python include dir
#   include_dir2 (variable): Output of found Python include dir2
#   packages_path (variable): Output of found Python packages path

function(find_python preferred_version min_version library_env include_dir_env
         found executable version_string version_major version_minor
         libs_found libs_version_string libraries library debug_libraries
         debug_library include_path include_dir include_dir2 packages_path)

if(NOT ${found})
  if(${executable})
    set(Python3_EXECUTABLE "${${executable}}")
  endif()

  find_package(Python3 "${preferred_version}" COMPONENTS Interpreter Development)
  if(NOT Python3_FOUND)
    find_package(Python3 "${min_version}")
  endif()

  if(Python3_FOUND)
    # Copy outputs
    set(_found ${Python3_FOUND})
    set(_executable ${Python3_EXECUTABLE})
    set(_version_string ${ython3_VERSION})
    set(_version_major ${Python3_VERSION_MAJOR})
    set(_version_minor ${Python3_VERSION_MINOR})
    set(_version_patch ${Python3_VERSION_PATCH})

    # Clear find_host_package side effects
    unset(Python3_FOUND)
    unset(Python3_EXECUTABLE CACHE)
    unset(Python3_VERSION_STRING)
    unset(Python3_VERSION_MAJOR)
    unset(Python3_VERSION_MINOR)
    unset(Python3_VERSION_PATCH)
  endif()

  if(_found)
    set(_version_major_minor "${_version_major}.${_version_minor}")

    if(NOT ANDROID AND NOT APPLE_FRAMEWORK)
      # not using _version_string here, because it might not conform to the CMake version format
      if(CMAKE_CROSSCOMPILING)
        # builder version can differ from target, matching base version (e.g. 2.7)
        find_package(Python "${_version_major_minor}" COMPONENTS  Interpreter Development)
      else()
        find_package(Python "${_version_major_minor}.${_version_patch}" EXACT COMPONENTS  Interpreter Development)
      endif()

      if(Python_FOUND)
        # Copy outputs
        set(_libs_found ${Python_Development_FOUND})
        set(_libraries ${Python_LIBRARIES})
        set(_include_path ${Python_INCLUDE_DIR})
        set(_include_dirs ${Python_INCLUDE_DIRS})
        set(_debug_libraries ${Python_LIBRARIES})
        set(_libs_version_string ${Python_VERSION})
        set(_debug_library ${Python_LIBRARY})
        set(_library ${Python_LIBRARY})
        set(_library_debug ${Python_LIBRARY})
        set(_library_release ${Python_LIBRARY})
        set(_include_dir ${Python_INCLUDE_DIR})
        set(_include_dir2 ${Python_INCLUDE_DIR2})

        # Clear find_package side effects
        unset(Python_Development_FOUND)
        unset(Python_LIBRARIES)
        unset(Python_INCLUDE_DIR)
        unset(Python_INCLUDE_DIRS)
        unset(Python_LIBRARIES)
        unset(Python_VERSION)
        unset(Python_LIBRARY CACHE)
        unset(Python_LIBRARY)
        unset(Python_LIBRARY_DEBUG)
        unset(Python_LIBRARY_RELEASE)
        unset(Python_LIBRARY CACHE)
        unset(Python_LIBRARY CACHE)
        unset(Python_LIBRARY CACHE)
        unset(Python_INCLUDE_DIR CACHE)
        unset(Python_INCLUDE_DIR2 CACHE)
      endif()
    endif()

    execute_process(COMMAND ${_executable} -c "from distutils.sysconfig import *; print(get_python_lib())"
                    RESULT_VARIABLE _cvpy_process
                    OUTPUT_VARIABLE _std_packages_path
                    OUTPUT_STRIP_TRAILING_WHITESPACE)
    if("${_std_packages_path}" MATCHES "site-packages")
      set(_packages_path "python${_version_major_minor}/site-packages")
    else() #debian based assumed, install to the dist-packages.
      set(_packages_path "python${_version_major_minor}/dist-packages")
    endif()
      if(EXISTS "${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX}/${${packages_path}}")
        set(_packages_path "lib${LIB_SUFFIX}/${_packages_path}")
      else()
        set(_packages_path "lib/${_packages_path}")
    endif()
  endif()

  # Export return values
  set(${found} "${_found}" CACHE INTERNAL "")
  set(${executable} "${_executable}" CACHE FILEPATH "Path to Python interpretor")
  set(${version_string} "${_version_string}" CACHE INTERNAL "")
  set(${version_major} "${_version_major}" CACHE INTERNAL "")
  set(${version_minor} "${_version_minor}" CACHE INTERNAL "")
  set(${libs_found} "${_libs_found}" CACHE INTERNAL "")
  set(${libs_version_string} "${_libs_version_string}" CACHE INTERNAL "")
  set(${libraries} "${_libraries}" CACHE INTERNAL "Python libraries")
  set(${library} "${_library}" CACHE FILEPATH "Path to Python library")
  set(${debug_libraries} "${_debug_libraries}" CACHE INTERNAL "")
  set(${debug_library} "${_debug_library}" CACHE FILEPATH "Path to Python debug")
  set(${include_path} "${_include_path}" CACHE INTERNAL "")
  set(${include_dir} "${_include_dir}" CACHE PATH "Python include dir")
  set(${include_dir2} "${_include_dir2}" CACHE PATH "Python include dir 2")
  set(${packages_path} "${_packages_path}" CACHE PATH "Where to install the python packages.")
endif()
endfunction(find_python)

set(MIN_VER_PYTHON2 2.7)
set(MIN_VER_PYTHON3 3.2)

#find_python(2.7 "${MIN_VER_PYTHON2}" PYTHON2_LIBRARY PYTHON2_INCLUDE_DIR
#    Python3_FOUND PYTHON2_EXECUTABLE PYTHON2_VERSION_STRING
#    PYTHON2_VERSION_MAJOR PYTHON2_VERSION_MINOR PYTHON2LIBS_FOUND
#    PYTHON2LIBS_VERSION_STRING PYTHON2_LIBRARIES PYTHON2_LIBRARY
#    PYTHON2_DEBUG_LIBRARIES PYTHON2_LIBRARY_DEBUG PYTHON2_INCLUDE_PATH
#    PYTHON2_INCLUDE_DIR PYTHON2_INCLUDE_DIR2 PYTHON2_PACKAGES_PATH)

find_python(3 "${MIN_VER_PYTHON3}" Python_LIBRARY Python_INCLUDE_DIR
    Python3_FOUND Python3_EXECUTABLE Python3_VERSION
    Python3_VERSION_MAJOR Python3_VERSION_MINOR PYTHON3LIBS_FOUND
    Python_VERSION Python_LIBRARIES Python_LIBRARY
    PYTHON3_DEBUG_LIBRARIES PYTHON3_LIBRARY_DEBUG Python_INCLUDE_DIR
    Python_INCLUDE_DIR Python_INCLUDE_DIR2 PYTHON3_PACKAGES_PATH)

if(PYTHON_DEFAULT_EXECUTABLE)
    set(PYTHON_DEFAULT_AVAILABLE "TRUE")
elseif(Python3_FOUND) # Use Python 2 as default Python interpreter
    set(PYTHON_DEFAULT_AVAILABLE "TRUE")
    set(PYTHON_DEFAULT_EXECUTABLE "${PYTHON2_EXECUTABLE}")
elseif(Python3_FOUND) # Use Python 2 as fallback Python interpreter (if there is no Python 2)
    set(PYTHON_DEFAULT_AVAILABLE "TRUE")
    set(PYTHON_DEFAULT_EXECUTABLE "${Python3_EXECUTABLE}")
endif()