Handling of the installation directory of some python subprojects fragile

[traversaro]

The logic of installation of Python bindings for some subprojects is inherently fragile. The superbuild computes the installation location of python bindings in

robotology-superbuild/CMakeLists.txt

Line 39 in 3d587be

string(STRIP ${_PYTHON_INSTDIR} ROBOTOLOGY_SUPERBUILD_PYTHON_INSTALL_DIR)

, via the code:

from distutils import sysconfig; print(sysconfig.get_python_lib(1,0,prefix=''))

Then, for some subprojects we explicitly set that the python installation should be the one that we set (for example casadi

robotology-superbuild/cmake/Buildcasadi.cmake

Line 33 in 3d587be

-DPYTHON_PREFIX:PATH=${ROBOTOLOGY_SUPERBUILD_PYTHON_INSTALL_DIR}

), however for some others we just rely on the fact that the subprojets also compute their python installation directory via from distutils import sysconfig; print(sysconfig.get_python_lib(1,0,prefix='')). However, this is fragile as the, for example, the directory returned by this code is different depending on whater we are running the code in the system python environment or in a virtual environment. We already had users realllllly confused by this.

A better alternative is to use a strategy similar to the one that we used for casadi.

fyi @LoreMoretti