Re: installing python 2 and python 3 in the same profile

[Pjotr Prins]

On Sun, Mar 11, 2018 at 12:10:09PM +0100, Ricardo Wurmus wrote:
> Obviously, I strongly disagree :)
 
You should ;)

> On my CentOS and Fedora machines at work both versions are installed
> (with the system package manager) and nobody complains.  I can conjure
> up a Python 2 environment by calling “python2” and a Python 3
> environment by calling “python3” or “python”.  Neither variant will load
> up modules for the other variant — unlike the behaviour on Guix.
> 
> Even in Guix we allow these packages to be added to the same environment
> with “guix environment --ad-hoc” – and there are no collisions, because
> upstream made the effort to ensure that these packages don’t provide
> files of the same names.
> 
> It is an unnecessary restriction to *prevent* users from installing
> Python 2 and 3 interpreters into the same profile.  Any errors we see
> with mixing 2 and 3 is due to a bug in Guix which is due to our use of
> PYTHONPATH.

Alright, if you choose to use them as two different tools/languages.

But even in minor versions there are problems. Ruby has those too, I
know for a fact, though Python may be worse since it uses compiled
sources.

> In large environments Python 2 and 3 modules and interpreters can
> peacefully coexist as long as the tools use the appropriate names for
> the interpreters (“python2” or “python” for Python 2, “python3” for
> the interpreter for Python 3).
> 
> In other places in Guix we don’t even prevent users from doing things
> that are generally ill-advised (e.g. the use of LD_LIBRARY_PATH); why
> would we prevent a perfectly valid use-case when it comes to different
> versions of Python?

Sure. Note that Python2 is quickly becoming obsolete. It is escalating
because packages are now dropping support. After 10 years of joy
mixing versions...

Pj.