cmake/Modules/FindPythonInterp.cmake

# - Find python interpreter
# This module finds if Python interpreter is installed and determines where the
# executables are. This code sets the following variables:
#
#  PYTHONINTERP_FOUND         - Was the Python executable found
#  PYTHON_EXECUTABLE          - path to the Python interpreter
#
#  PYTHON_VERSION_STRING      - Python version found e.g. 2.5.2
#  PYTHON_VERSION_MAJOR       - Python major version found e.g. 2
#  PYTHON_VERSION_MINOR       - Python minor version found e.g. 5
#  PYTHON_VERSION_PATCH       - Python patch version found e.g. 2
#
#  Python_ADDITIONAL_VERSIONS - list of additional Python versions to search for

#=============================================================================
# Copyright 2005-2010 Kitware, Inc.
# Copyright 2011 Bjoern Ricks <bjoern.ricks@gmail.com>
#
# Distributed under the OSI-approved BSD License (the "License");
# see accompanying file Copyright.txt for details.
#
# This software is distributed WITHOUT ANY WARRANTY; without even the
# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the License for more information.
#=============================================================================
# (To distribute this file outside of CMake, substitute the full
#  License text for the above reference.)

# Search for the current active python version first
find_program(PYTHON_EXECUTABLE NAMES python)

# Set up the versions we know about, in the order we will search. Always add
# the user supplied additional versions to the front.
set(_Python_VERSIONS
  ${Python_ADDITIONAL_VERSIONS}
  2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 1.6 1.5)

# Search for newest python version if python executable isn't found
if(NOT PYTHON_EXECUTABLE)
    foreach(_CURRENT_VERSION ${_Python_VERSIONS})
      set(_Python_NAMES python${_CURRENT_VERSION})
      if(WIN32)
        list(APPEND _Python_NAMES python)
      endif()
      find_program(PYTHON_EXECUTABLE
        NAMES ${_Python_NAMES}
        PATHS [HKEY_LOCAL_MACHINE\\SOFTWARE\\Python\\PythonCore\\${_CURRENT_VERSION}\\InstallPath]
        )
    endforeach()
endif()

# determine python version string
if(PYTHON_EXECUTABLE)
    execute_process(COMMAND "${PYTHON_EXECUTABLE}" --version ERROR_VARIABLE _VERSION OUTPUT_QUIET ERROR_STRIP_TRAILING_WHITESPACE)
    string(REPLACE "Python " "" PYTHON_VERSION_STRING "${_VERSION}")
    string(REGEX REPLACE "^([0-9]+)\\.[0-9]+\\.[0-9]+.*" "\\1" PYTHON_VERSION_MAJOR "${PYTHON_VERSION_STRING}")
    string(REGEX REPLACE "^[0-9]+\\.([0-9])+\\.[0-9]+.*" "\\1" PYTHON_VERSION_MINOR "${PYTHON_VERSION_STRING}")
    string(REGEX REPLACE "^[0-9]+\\.[0-9]+\\.([0-9]+).*" "\\1" PYTHON_VERSION_PATCH "${PYTHON_VERSION_STRING}")
endif()

# handle the QUIETLY and REQUIRED arguments and set PYTHONINTERP_FOUND to TRUE if
# all listed variables are TRUE
include(${CMAKE_CURRENT_LIST_DIR}/FindPackageHandleStandardArgs.cmake)
FIND_PACKAGE_HANDLE_STANDARD_ARGS(PythonInterp REQUIRED_VARS PYTHON_EXECUTABLE VERSION_VAR PYTHON_VERSION_STRING)

mark_as_advanced(PYTHON_EXECUTABLE)