[Nix-dev] Fwd: Python 3 as default

[Freddy Rietdijk]

> I'd be happy to help with the process of mass-renaming, if somebody
provided a list of packages wanting 2 or 3, however I suspect the real work
is in determining those package sets.
So, if a query-replace for `pkgs.python` -> `pkgs.python2` / `pkgs.python3`
within nixpkgs would cause so much trouble, how would a rename in
`all-packages.nix` fare any better? Are we ready to throw the switch yet?

All the packages that explicitly need Python 2 are already pinned to use
Python 2. That was a matter of converting, testing, and moving on. About
150 packages were pinned to `python2`. That is why a `python = python3`
won't break anything (or nearly nothing) in Nixpkgs anymore.

Explicitly pinning to `python3` means converting every expression that has
`python` to `python3`. No breakage should occur anymore, except when one
makes a mistake in converting expressions only partially. There are about
1000 packages that need to be converted.

The best method I can think of is searching for all the files that contain
`python` without leading and trailing alphanumerical characters. Those can
typically be converted to `python3`. Exceptions are
`pkgs/top-level/python-packages.nix`,
`pkgs/development/interpreters/python`,
 `pkgs/development/python-modules/*` and when the `python` argument is
overriden in, say, `all-packages.nix`. Another exception could be `python =
python3.withPackages(...)` but I think that is rare.

On Fri, Feb 24, 2017 at 4:59 AM, Herwig Hochleitner <hhochleitner at gmail.com>
wrote:

> And a copy for the list as well + a one person applause for our
> friend, reply-all.
>
> ---------- Forwarded message ----------
> From: Herwig Hochleitner <hhochleitner at gmail.com>
> Date: 2017-02-24 4:54 GMT+01:00
> Subject: Re: [Nix-dev] Python 3 as default
> To: Freddy Rietdijk <freddyrietdijk at fridh.nl>
>
>
> First off, for context: I'm very grateful for your work to get our
> python stuff over to python3.
>
> I also support python3 providing `/bin/python`, _if_ we ensure that
> python2's `/bin/python` takes precedence in all collisions (right
> until python2's EOL). I think the PEP's symlinking guideline doesn't
> directly apply here, since our transitive dependencies don't collide
> (horray!).
>
> I'm against changing pkgs.python to mean python3, though. Let me break
> down why:
>
> 2017-02-22 16:32 GMT+01:00 Freddy Rietdijk <freddyrietdijk at fridh.nl>:
> >
> >
> > If we can't break stuff we might as well not make any changes at all.
>
>
> I see your point, but I'd like to point out that additive changes are
> less cumbersome than breaking changes, and explicit breakage is less
> cumbersome than implicit breakage.
>
> > the fact that upstream wants everyone to move away from Python 2
>
> to be fair, upstream has been wanting that for a decade
>
> >
> > incompatibilities also exist between minor versions
>
>
> i think users are customarily expected to keep up with point releases.
>
> > explicitly changing parameters and arguments ... considering how much
> Python is used throughout Nixpkgs that's just unrealistic.
> >
> > I'm still open to getting rid of the `python` attribute, ... If this is
> the route we want to take, then its very unlikely we will be able to switch
> to 3.5 as the default for 17.03,
>
>
> I'd be happy to help with the process of mass-renaming, if somebody
> provided a list of packages wanting 2 or 3, however I suspect the real
> work is in determining those package sets.
> So, if a query-replace for `pkgs.python` -> `pkgs.python2` /
> `pkgs.python3` within nixpkgs would cause so much trouble, how would a
> rename in `all-packages.nix` fare any better? Are we ready to throw
> the switch yet?
>
> > or 3.6 for 17.09.
>
>
> Are there python projects, stuck at 3.5, as well?
>
> kind regards
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>
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