Compiling wrappers for multiple versions of Python

When multiple versions of Python are installed and/or Boost Python are installed, the include directories and libraries might be incorrectly detected. Such a case can be easily detected by looking at the dependencies (e.g. odil.so or odil.dylib) of the library in the wrappers subdirectory of the build directory: platform-dependent tools such as ldd Linux) or otool (OS X) will show version discrepancies between the Python library (e.g. libpython3.4m.so) and the Boost.Python library (e.g. libboost_python-py27.so). Since the naming conventions are not consistent across platforms, it is up to the user to override compile settings in such cases.

The Python version can be forced using TODO. For fine-tuning, PYTHON_INCLUDE_DIR and PYTHON_LIBRARY may also be used. The Boost.Python version can be forced using Boost_PYTHON_LIBRARY_DEBUG and Boost_PYTHON_LIBRARY_RELEASE.

For example, on Debian 8 (jessie), the following (broken) CMake invocation selects Python 3.4 with the 2.7 version of Boost.Python:

cmake -D Python_ADDITIONAL_VERSIONS=3.4 ${SOURCE_DIRECTORY}

Assuming that BOOST_PYTHON_34 contains the location of the 3.4 version of Boost.Python (e.g. /usr/lib/x86_64-linux-gnu/libboost_python-py34.so), the correct invocation of CMake reads:

cmake -D Python_ADDITIONAL_VERSIONS=3.4 -D Boost_PYTHON_LIBRARY_DEBUG=${BOOST_PYTHON_34} -D Boost_PYTHON_LIBRARY_RELEASE=${BOOST_PYTHON_34} ${SOURCE_DIRECTORY}