Hi, as announced in https://lists.gnu.org/archive/html/guix-devel/2021-01/msg00021.html I’ve been working on adding an additional phase to Python packages to check whether they actually work. I cleaned up my patch, added tests and now I’m pretty confident it works as expected. The first patch in this series adds this phase, while the other ones fix build failures caused by it. All of this should go to core-updates (or a separate wip-* branch?), since it causes a massive number of rebuilds. You can also pull my git repo at https://github.com/PromyLOPh/guix.git branch work-python-importcheck. Cheers, Lars