Ah, interesting. The install-time generation case is even trickier, since you presumably can't force in-place regeneration of existing pyc files on systems that previously had 3.5.2 and upgraded to 3.5.3.

When I last spoke to Peter about this yesterday, he was exploring the idea of a downstream-only patch to 3.5.3 that gave it the ability to load pyc files that used the 3.5.2 magic number (so it would *emit* files with the new magic number, but still allow use of pyc files with the old one). Assuming he can get that to work, then I guess it may be of interest to Debian & Ubuntu as well.