Thank you for replying (and by the way thank you for this great library)
(Initially because I needed to compile some old code urgently (which worked like a charm on a version I had compiled on some old windows distro), I thought "great there's a ppa let's use that !")
"elemental-mpich-python2" installs without error messages, however my old code ran into trouble confirmed by test examples.
Therefore I built it from source (after apt-get remove "elemental-mpich-python2" !) also because I wasn't sure that the ppa would make the link with libflame correctly.