[rdo-dev] Managing executables in python2/python3 packages

Alan Pevec apevec at redhat.com
Tue Jun 26 21:10:30 UTC 2018

On Tue, Jun 26, 2018 at 7:53 PM, Alfredo Moralejo Alonso
<amoralej at redhat.com> wrote:
> As part of the python3 PoC we are working on in rocky cycle i think we need
> to reconsider how we are managing executables in packages with
> python2/python3 subpackages. Currently, we are following Fedora best
> practices creating <executable>-<python version> in python{2|3}-<package>
> packages and making <executable> a symlink for python2 version and shipping
> it only in python2 subpackages.

This mess is only required when you have both python2 and python3 subpackage,
idea was to switch to python3 fully in Fedora and drop python2 as per
recent Fedora packaging guideline change
https://pagure.io/packaging-committee/issue/753 "python2-... should
not be packaged when it's not needed"

Unversioned <executable> binary then links to the python3 version:

> I think this is not a convenient way to manage it for python3 installations
> as it requires users (and tools) to use <executable>-3 commands. IMO, moving
> from python2 to python3 should be more transparent from a user PoV.
> I see some ways we could manage this:
> 1. Don't build python2 in el7 builds and stop creating <executable>-<python
> version>, just <executable>.

el7? Did you mean, Fedora? If so, yes, this is solution, as explained above.

> 2. Keep building both and change <executable> symlink to point to
> <executable>-3 when python3 subpackages are enabled in spec file.

no, that's against the current Fedora packaging guidelines, which are
following upstream Python requirement that unversioned "python"
executes "python2"

> 3. Keep building both and use alternatives mechanism to manage <executable>
> symlink to point to <executable>-2 or <executable>-3 depending on what is
> installed (-3 if both are enabled).

NACK, same as 2.

> My main doubt is related to how to handle this from a Fedora perspective
> keeping in mind that we are using the same specs to build packages in Fedora
> repos. I guess the best way to keep both python2 and 3 installations working
> is to use option 3.

We really do not want to maintain the mess of mixed py2/3 - in Fedora
all should move to python3,
while keeping py2 compat for EL7 builds. Looking at how much
copy/paste there is between py2/3 sections, I wonder if we could just
generate python3 spec from the python2, with some mappings in Requires
using pymod2pkg ?


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