[Nix-dev] Python 3 as default

[Richard Ipsum]

Hi,

from this and some of the discussion above I see that the situation
in NixOS may be a little different to most other distros.

I agree that you probably don't want to have to patch all shebangs manually,
but making python2 take priority over python3 in the case of a collision
seems like a good solution.

Anyway I really just wanted to raise the point for discussion,
having done that I can go back to lurking on this list! :)

Thanks,
Richard

On Tue, Feb 14, 2017 at 01:17:07PM +0100, Freddy Rietdijk wrote:
> Sure. As I said the PEP doesn't provide any method for distributions that
> would already like to make the switch. In an ideal scenario all developers
> would update their requirements/shebangs. That just doesn't happen.
> 
> What we perhaps ought to do is instead fix all those shebangs ourselves,
> before we run `patchShebang/wrapPythonPrograms`. Considering the amount of
> (boring) work that takes I don't see anyone stepping up doing that.
> Therefore, symlinking `python` *also* to `python3` is a pragmatic solution.
> 
> As Moritz described, we already pass a specific interpreter as a buildInput
> to a package. Therefore, there shouldn't be any issues with our programs.
> The only issue that could arise is when one installs both interpreters in
> one profile. In that case a collision occurs. Maybe we should set a
> priority here so that in that case `python` will refer to `python2`.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> On Tue, Feb 14, 2017 at 12:11 PM, Richard Ipsum <richardipsum at fastmail.co.uk
> > wrote:
> 
> > On Tue, Feb 14, 2017 at 11:29:32AM +0100, Freddy Rietdijk wrote:
> > > Hi Richard,
> > >
> > > Thanks for sharing the PEP.
> > >
> > > Actually, we, or at least I, chose to ignore that PEP, and so we do
> > > symlink.
> > >
> >
> > Out of interest can I ask what the rationale for that decision is?
> >
> > I'd like to try to persuade you not to symlink python to python3,
> > because doing so potentially breaks existing python2 programs.
> >
> > But since I'm not an active contributor to this project it's not my place
> > to argue here really. :)
> >
> > Thanks,
> > Richard
> >
> > [snip]
> > >
> > >
> > > On Tue, Feb 14, 2017 at 10:40 AM, Richard Ipsum <
> > richardipsum at fastmail.co.uk
> > > > wrote:
> > >
> > > > On Mon, Feb 13, 2017 at 10:08:07AM +0100, Freddy Rietdijk wrote:
> > > > > Hi,
> > > > >
> > > > > As you may be aware the plan is to change to Python 3.5 as default
> > for
> > > > > 17.03. There were a couple of things that had to be done, and I think
> > > > we're
> > > > > ready now to make the change. Packages that require Python 2 are now
> > > > pinned
> > > > > to do so.
> > > > >
> > > > > Now, obviously I haven't been able to test all packages myself, but
> > > > judging
> > > > > from what Hydra reports and from working from the `python3` branch I
> > > > don't
> > > > > expect any major issues.
> > > > >
> > > > > The Python 2.7 interpreter had quite some patches, among one to make
> > the
> > > > > interpreter and Python packages more deterministic. I say more,
> > because
> > > > > they're not fully deterministic yet. I have some patches lining up
> > for
> > > > the
> > > > > 3.5 interpreter to improvement determinism there as well.
> > > > >
> > > > > In any case, I would like to merge this as soon as possible. Any
> > > > objections?
> > > > >
> > > > > Freddy
> > > >
> > > > Hi, I'm not really an active contributor here but I follow NixOS
> > because
> > > > I think it's a really cool project.
> > > >
> > > > Am I to understand that NixOS is considering replacing the python2
> > > > interpreter with the python3 interpreter, as arch did?
> > > >
> > > > If that's the case it may be worth considering this pep[1] first.
> > > >
> > > > If I've misunderstood and there's no intention to symlink 'python' to
> > > > 'python3'
> > > > then please ignore this. :)
> > > >
> > > > [1]: http://legacy.python.org/dev/peps/pep-0394/#id5
> > > > _______________________________________________
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> > > > nix-dev at lists.science.uu.nl
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> > > >
> >