(First of all, is there a typo in "_libBorAgainFit.so"?) yes I forgot the n of born :) [...] > I expect that in the case of bornagain, libBornAgainFit.py looks for > _libBornAgainFit.so in the same directory, > /usr/lib/python3/dist-packages/bornagain/. yes and /usr/bin/bornagain also look for these library. this why I am asking, where to put a library wchih is sort of private... Cheers Frederic