* Create Python modules eccodes and gribapi already in the source tree
* Copy modules to build tree, so build tree mirrors install location
* Call `python setup.py build_exit --inplace` to build extension module
for use in build tree (using the build tree RPATH)
* Call `python setup.py install --prefix=${CMAKE_INSTALL_PREFIX}` to
install (using the build tree RPATH)
The build tree is now a fully functioning Python package, so you can
also `pip install /path/to/eccodes/build/python`.
Florian Rathgeber