Changing default interpreter means some applications will stop functioning and this may mean passing python = python37; will be needed, although preferably the application is made compatible with 3.8.
A large update to the package set has not happened in a long time, which means by now it is quite outdated. It’s important the core set of packages is fairly up to date, especially prior to a NixOS release. After this update I expect a somewhat smaller update again prior to the 20.09 release.
Now, given how tightly the packages are connected it’s typically a lot of work to get everything fixed up. My focus is on the core packages so this means there will be breakage in leaf packages. Also important to consider is that many packages have dropped Python 2 support. In those cases, we can provide an older version for Python 2, but of course someone will need to step up to make that happen. As part of this change I intend to provide Python 2 versions of core packages, but not more than that.
If you like to help out, please have a look at the PR. There should not be any more force pushes to that branch for at least the coming days.
One thing I forgot to mention is that, while by now the far majority of packages are compatible with 3.8, not all are. I think most importantly aiohttp is still stuck at 3.7.
python38 is now the default python3 interpreter on master. Note there will be regressions, certain applications will fail to build with Python 3.8. They either need to be made compatible with 3.8 (preferred solution) or use 3.7 instead.
Note some are fixed on current staging-next. Thus it is best to wait with fixing these applications on master or opening PR’s towards staging-next.
Are there any plans on deprecating/phasing out Python 2? Python 2 is now unsupported and has an slowly increasing backlog of security issues which will possibly not receive upstream fixes.
I think originally it was going to be a soft deprecation, as many applications (such as sage or calibre) still used python2 at the time. But if there’s active CVE’s that are out, then I think that warrants at least marking the package as insecure, as mentioned in the thread. However, I’ll defer to @FRidh on any actionable items.
What would deprecating / phasing out Python 2 mean? In principle we try to avoid Python 2. Indeed, most of Nixpkgs can be built without, leaving only relatively rarely used packages that depend on Python 2.
The plan is to keep the Python 2 interpreter around, and at least a set of core packages. Exactly how many or which entirely depends on the community; if they need packages they need to maintain them. The Python 2 package set is also increasingly diverging from the Python 3 set in terms of versions.
Will there be security issues with them? Yes, likely, but that’s up to the users to accept or not.
Note I won’t bother with patching Python 2 or any of its packages, that will be up to those that want to use it.