[Bug 1958720] Re: python3-yaml and python3-six are not co-installable with python-is-python2 in jammy

[Robie Basak]

I did some research to ensure that removing the Breaks is safe. Some of
this repeats what we covered already but I'm stating it again so my
logic is self-contained here.

If python-is-python2 is installed on Focal and I upgrade to Jammy, then
python-is-python2 gets removed because of the Breaks.

If python-is-python2 is installed on Impish and I upgrade to Jammy using
do-release-upgrade, then python-is-python2 remains but the installer
offers to remove it as obsolete. I can refuse, however.

Therefore, by adjusting things so that in the upgrade from Focal to
Jammy python-is-python2 can stay installed, I'm not changing behaviour
from what the Impish to Jammy upgrade allows anyway. Note that the user
will still need to state that they don't want to remove obsolete
packages. This is the default if you just press Return.

On Jammy, python3-yaml (src:pyyaml) Breaks python (<< 2.7.18)
On Jammy, python3-six (src:six) Breaks python (<< 2.7.18)

On Focal, python-is-python2 Provides python (= 2.7.17-1)
On Impish, python-is-python2 Provides python (= 2.7.18-2)
Nothing else on Focal nor Impish Provides python.
python is not a concrete package on Focal nor Impish.
On both Focal and Impish, python-is-python2 Depends on python2 but has no Depends or Recommends on any other package.

Therefore the only impact of this change will be against the python-is-
python2 package and I don't expect there to be unexpected interactions
with any other package by removing the Breaks.

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https://bugs.launchpad.net/bugs/1958720

Title:
  python3-yaml and python3-six are not co-installable with python-is-
  python2 in jammy

Status in pyyaml package in Ubuntu:
  Incomplete
Status in six package in Ubuntu:
  New

Bug description:
  The packages python3-yaml and python-is-python2 are not co-installable
  in jammy and I believe they should be.  This currently prevents me
  from upgrading one of my machines from focal to jammy.

  Further analysis with the help of Stefano Rivera revealed that what-
  is-python no longer produces a python-is-python2 package and the
  changelog hints at that being intentional.  Jammy still has a python2
  package, though.

  python3-yaml in jammy breaks on python (<2.7.18).  The python-is-
  python2 package in focal is version 2.7.17-4 and in impish it is
  2.7.18-9 and thus will be forcefully removed when going to jammy.

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