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Re: Bug#901001: python3-minimal should Pre-Depend on python3.N-minimal

On Sat, Jun 09, 2018 at 06:39:19PM +0200, Matthias Klose wrote:
> On 09.06.2018 18:31, Matthias Klose wrote:
> > On 09.06.2018 11:55, Philipp Kern wrote:
> > > On 6/9/18 7:20 AM, Steve Langasek wrote:
> > > > - the package is being upgraded; it is in the common case (when no python
> > > >    module names have been dropped from within the package) less important to
> > > >    run py3clean because the same files will be recreated shortly afterwards
> > > >    by py3compile from the new postinst.

> > > What's the consequence from deleting the files and only recreating them
> > > later? Longer startup time of the interpreter in that short window?

> > yes, that's the only thing.

> > > Because if it's worse, it'd be good to have py3clean only delete the
> > > obsolete files in the postinst?

> but as written in the bug report, there is another solution, to have
> py3clean search for the interpreter it uses, and which doesn't need the
> pre-dependency.

Is the following scenario a concern that we should take into consideration?

 - a core library that python3.5-minimal (or libpython3.5-minimal) depends
   on has an ABI change and must be renamed, with a conflicts on the old
   package name.
 - new python-minimal is unpacked. /usr/bin/python is a dangling symlink.
 - python3.5-minimal is removed due to the conflict.
 - python3.6-minimal is not yet unpacked, because ordering is not
 - python3-foo module is removed due to another conflict.  The prerm fails
   because py3clean can find no version of python3 interpreter on the disk.

The pre-depends would address this case, by enforcing the configuration of
python3.6-minimal before unpacking python-minimal (and before removing
python3.5-minimal).  It does constrain apt's solver, but as long as apt can
find a solution, that's ok.

It may be an ignorable hypothetical, since the set of libraries that
python3.5-minimal + libpython3.5-minimal depends on is quite small, and they
are all very stable and well-maintained upstream (zlib, libexpat1, libc6,

Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                   https://www.debian.org/
slangasek@xxxxxxxxxx                                     vorlon@xxxxxxxxxx

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