[Nix-dev] multiple versions of the same software? / collisions

[Freddy Rietdijk]

A method to have access to all interpreters is to create a derivation that
has symbolic links to each of the interpreters and install that one. But as
has been said before nix-shell is the recommended method.



On Thu, Aug 4, 2016 at 2:13 PM, Rok Garbas <rok at garbas.si> wrote:

> for the python development don't use nix-env but create per project
> default.nix scripts and use nix-shell.
>
> make sure you read the python section in nixpkgs manual ->
> http://nixos.org/nixpkgs/manual/
>
> if you're looking to generate nix expressions from requirements.txt
> checkout pypi2nix -> https://github.com/garbas/pypi2nix. also know
> that pypi2nix is in early stage - still it is giving good results for
> some - and i'm looking for feedback of packages that break since this
> is the only way i can fix it.
>
>
> On Thu, Aug 4, 2016 at 2:07 PM, Guillaume Maudoux (Layus)
> <layus.on at gmail.com> wrote:
> > Hi,
> >
> > I think you are putting your efforts in the wrong direction.
> > Nix is not designed to install both python 3.4 and 3.5 in the same
> > environment.
> >
> > What it can do however is cache both in the store, so you can get an
> > environment with python 3.4 with
> > nix-shell -p python34
> > and an environment with python 3.5 with
> > nix-shell -p python35
> >
> > Nix can provide you with as many different environments at the same time.
> > You can have a shell with python 3.4 running besides a shell with python
> > 3.5.
> > You should however not install both in your default environment (nix-env
> > -i) as it won't work.
> >
> > May I refer you to https://nixos.org/wiki/Development_Environments ?
> >
> > Regards,
> > -- Layus.
> >
> >
> > Le 03/08/16 à 16:43, Roland Koebler a écrit :
> >> Hi,
> >>
> >> I think I've now found out (at least partially), although this could
> >> result in a package being installed multiple times.
> >>
> >>> It appears that the flag setting only works on already installed
> packages.
> >> Yes, and if I use
> >>
> >>     $ nix-env -i python3-3.5.2
> >>     ...
> >>     $ nix-env --set-flag priority 10 python3-3.5.2
> >>     ...
> >>     $ nix-env -i python3-3.4.5 python3-3.5.2
> >>     replacing old ‘python3-3.5.2’
> >>     installing ‘python3-3.4.5’
> >>     installing ‘python3-3.5.2’
> >>
> >> it does not work, since the last command first removes python3-3.5.2,
> >> then probably the flag is lost, and then installs it again.
> >>
> >>> Also I'm not sure, but even if there are name collisions in the user
> >>> environment, it should still be possible to install both packages but
> only
> >>> use one of the names, and then create your name alias to the non-named
> >>> package. However I do not know how this can be done.
> >> I think I've found out. The following works:
> >>
> >>     $ nix-env -i python3-3.5.2
> >>     $ nix-env --set-flag priority 10 python3-3.5.2
> >>     $ nix-env -i -P python3-3.4.5
> >>
> >> --preserve-installed / -P was the relevant switch.
> >> However, this can have some strange side-effects, since -P can
> >> cause a package to be installed "multiple times":
> >>
> >>     $ nix-env -i -P python3-3.4.5
> >>     ...
> >>     $ nix-env -i -P python3-3.4.5
> >>     ...
> >>     $ nix-env -i -P python3-3.4.5
> >>     ...
> >>     $ nix-env -q
> >>     ...
> >>     python3-3.4.5
> >>     python3-3.4.5
> >>     python3-3.4.5
> >>     python3-3.4.5
> >>     ...
> >>
> >> This could then be "resolved" by:
> >>
> >>     $ nix-env -e python3-3.4.5
> >>     uninstalling ‘python3-3.4.5’
> >>     uninstalling ‘python3-3.4.5’
> >>     uninstalling ‘python3-3.4.5’
> >>     uninstalling ‘python3-3.4.5’
> >>     $ nix-env -P -i python3-3.4.5
> >>     installing ‘python3-3.4.5’
> >>
> >> But it still looks strange.
> >> Is this intentional?
> >>
> >> Roland
> >>
> >> _______________________________________________
> >> nix-dev mailing list
> >> nix-dev at lists.science.uu.nl
> >> http://lists.science.uu.nl/mailman/listinfo/nix-dev
> >
> > _______________________________________________
> > nix-dev mailing list
> > nix-dev at lists.science.uu.nl
> > http://lists.science.uu.nl/mailman/listinfo/nix-dev
>
>
>
> --
> Rok Garbas
> https://garbas.si
> _______________________________________________
> nix-dev mailing list
> nix-dev at lists.science.uu.nl
> http://lists.science.uu.nl/mailman/listinfo/nix-dev
>
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