Migrate to Python 3 as default install

[domenkozar]

• Remove bloated Python modules such as tcl/tk (see Python 2 how it's done)
• identify python2 dependencies in common environments (server,kde,gnome,e17)
• Migrate nixos/modules/system/boot/loader/systemd-boot (or alternatively, seems simple enough to rewrite in some other language)

[abbradar]

I wanted to create this issue long ago and help with what I can, but hasn't found time ~_^

[FRidh]

We should have for each interpreter version a

• python which is the full version
• python-stripped which is commonly used in other packages
  and package sets for each.

[aneeshusa]

I have used my nixpkgs config to set Python 3 as the default, and have only encountered a few packages requiring Python 2 so far. I can help put in PRs to make sure they use python2 (or python2.tiny / python2.small / python2-stripped ) instead of python3.

Maybe the python infra should automatically use the smaller version when python/python2 is a build input?

[edolstra]

Regarding systemd-boot, I started rewriting it in Perl a while back, but it's not entirely finished yet. I can pick that up.

Other than that, what exactly does it mean to have Python 3 as the "default install" given that NixOS doesn't install Python by default (AFAIK)?

[FRidh]

pkgs.python = pkgs.python3 instead of pkgs.python = pkgs.python2, and likely pkgs.python3 = pkgs.python35 although we could try 3.6 as well; there aren't going to be many changes from 3.5 to 3.6. This change will impact a lot of packages/services.

[domenkozar]

@edolstra it means that for graphical stacks we have only python3 in the closure. So Python 3 should be the default interpreter used in applications.

[domenkozar]

nixos/modules/system/boot/loader/systemd-boot can be easily ported to python3, unless you want to maintain it in perl @edolstra

[FRidh]

is there a test for systemd-boot?

[vcunat]

Many packages use python in their build system. I don't know how well python3 is supported for that, generally.

[dezgeg]

is there a test for systemd-boot?

There is tests.boot.simpleUefiGummiboot. It's not a release blocker currently though.