Packaging issue with Python 3 on Fedora

[bochecha]

I'm trying to package Pew for Fedora.

I have a repository with work-in-progress packages, however one thing is problematic.

I've chosen to build Pew for Python 3, because at this point I'd rather not do anything related to Python 2 if I don't have to. 😉

So I built Pew and its dependencies as Python 3 modules, and overall everything is working fine... except one tiny little detail.

    try:
        check_call(["virtualenv", envname] + rest, cwd=str(workon_home))
    except (CalledProcessError, KeyboardInterrupt):
        ...

The /usr/bin/virtualenv command on Fedora is the Python 2 version. For Python 3, the command is /usr/bin/virtualenv-3.4.

As a result, even though I've built Pew for Python 3, I still need to add a dependency on the Python 2 version of virtualenv. 😞

This virtualenv/virtualenv-3.4 issue is Fedora-specific, as far as I know (Debian only ships /usr/bin/virtualenv for the Python 3 version it seems), so I'd understand if that's not something you want to work around upstream.

Possible solutions I can think of include:

• If the virtualenv command doesn't exist, try virtualenv-3.4, or virtualenv-3.5, or... Which is clearly not very smart.
• Stop subprocess-ing the command, and instead use a Python module (maybe venv for Python >= 3.3 ?)
• A downstream, Fedora-only patch. (this would probably be the worst solution, but I figured I'd mention it... let's find something better)
• Building Pew for Python 2 on Fedora

What do you think?

[berdario]

Hi, sorry for not replying earlier. I think there has also been a discussion via email, but I'd like to mention a couple of things here:

• I think that the proper solution is to use Alternatives (see also an example of how this is used to select a java version). This way Pew would depend on a virtual-package/meta-package "virtualenv", and the python2-virtualenv, python3.4-virtualenv python3.5-virtualenv could all of them be providing it. /usr/bin/virtualenv would thus be a symlink to the preferred package installed by the user
• I planned to use venv, but I think it might still be a bit premature. Stop subprocess-ing is also something that I considered doing, and back in February I hoped that virtualenv-rewrite would be the way forward (so I refrained from doing any change in that direction until the new virtualenv would've been ready, but I don't think that'll really materialize )

Btw, due to how distracted I've been, if you want I can give you commit access to fix some things (like, falling back on /usr/bin/virtualenv-3.4 or stop subprocess-ing) to help your packaging effort, without having me as a blocker, but I understand also if in the meanwhile you might've moved on and started some other effort.

[berdario]

PS: I forgot to mention...

there's another reason why I haven't bothered with an alternative to subprocess-ing virtualenv

[bochecha]

I think that the proper solution is to use Alternatives (see also an example of how this is used to select a java version).

I know of the alternatives framework, we use it quite a bit in Fedora as well.

However, as it turns out that's not how /usr/bin/virtualenv is packaged in Fedora. Maybe it should be, though. (I'm generally not a big fan of how we've handled the Python3 versions of tools like pip, easy_install and virtualenv, which are suffixed with a 3...)

I'll try and ask if this can be improved on the Fedora side.

Btw, due to how distracted I've been, if you want I can give you commit access to fix some things (like, falling back on /usr/bin/virtualenv-3.4 or stop subprocess-ing) to help your packaging effort, without having me as a blocker, but I understand also if in the meanwhile you might've moved on and started some other effort.

I haven't, I'm still very happy using pew. 😄

[berdario]

Good :)

Let me know if you find a resolution.

Anyhow, it should also be possible to have a Python3-pew packaged in Fedora that depends on the Python2-virtualenv package, shouldn't it?

It's not pretty, but it should be a problem that it'll sort itself, as soon as Fedora drops Python2

[bochecha]

Anyhow, it should also be possible to have a Python3-pew packaged in Fedora that depends on the Python2-virtualenv package, shouldn't it?

That is in fact how I "solved" this problem a few weeks ago. 😉

[bochecha]

This was fixed by 999674c

Thanks @berdario !

[meshy]

I think you're right, it looks as though that commit fixed this. I hope you don't mind if I close this issue as a result!