Changes/Python3.12

Python 3.12

Summary

Update the Python stack in Fedora from Python 3.11 to Python 3.12, the newest major release of the Python programming language.

Owner

• Name: Tomáš Hrnčiar
• Name: Miro Hrončok
• Name: Lumír Balhar
• Email: python-maint@redhat.com

Current status

• Targeted release: Fedora Linux 39
• Last updated: 2023-07-05
• devel thread
• FESCo issue: #2890
• Tracker bug: #2135404
• Release notes tracker: #903

Detailed Description

We would like to upgrade Python to 3.12 in Fedora 39 thus we are proposing this plan early.

See the upstream notes at Features for 3.12 and What's new in 3.12.

Important dates and plan

• 2022-05-08: Python 3.12 development begins
• 2022-10-24: Python 3.12.0 alpha 1
  • Package it as python3.12 for testing purposes
  • Start the bootstrap procedure in Copr
  • Do a mass rebuild against every future release in Copr
• 2022-11-14: Python 3.12.0 alpha 2
• 2022-12-05: Python 3.12.0 alpha 3
• 2023-01-09: Python 3.12.0 alpha 4
• 2023-02-06: Python 3.12.0 alpha 5
• 2023-02-07: Branch Fedora 38, Rawhide becomes future Fedora 39
  • The earliest point when we can start rebuilding in Koji side-tag
• 2023-03-06: Python 3.12.0 alpha 6
• 2023-04-03: Python 3.12.0 alpha 7
• 2023-05-08: Python 3.12.0 beta 1
  • No new features beyond this point
• 2023-05-29: Python 3.12.0 beta 2
  • The ideal point when we can start rebuilding in Koji
• 2023-06-05: Expected side tag-merge (optimistic)
• 2023-06-19: Python 3.12.0 beta 3
• 2023-06-26: Expected side tag-merge (realistic)
• 2023-07-10: Python 3.12.0 beta 4
• 2023-07-17: Expected side tag-merge (pessimistic)
• 2023-07-19: Fedora 39 Mass Rebuild
  • The mass rebuild happens with the fourth beta. We might need to rebuild Python packages later in exceptional case.
  • If the Koji side-tag is not merged yet at this point, we defer the change to Fedora 40.
• 2023-07-31: Python 3.12.0 candidate 1
  • This serves as "final" for our purposes.
• 2023-08-08: Branch Fedora 39, Rawhide becomes future Fedora 40
• 2023-08-08: Fedora 39 Change Checkpoint: Completion deadline (testable)
• 2023-08-22: Fedora Beta Freeze
  • If rebuild with 3.12.0rc1 is needed, we should strive to do it before the freeze - there is a window of 3 weeks.
• 2023-09-04: Python 3.12.0 candidate 2
• 2023-09-12: Fedora 39 Beta Release (Preferred Target)
  • Beta will likely be released with 3.12.0rc2.
• 2023-09-19: Fedora 39 Beta Target date #1
• 2023-10-02: Python 3.12.0 final
• 2023-10-03: Fedora 39 Final Freeze
  • We'll update to 3.12.0 final using a freeze exception.
• 2023-10-17: Fedora 39 Preferred Final Target date
• 2023-10-24: Fedora 39 Final Target date #1

(From Python 3.12 Release Schedule and Fedora 39 Release Schedule.)

The schedule might appear somewhat tight for Fedora 39, but Python's annual release cycle was adapted for Fedora and this worked fine since Python 3.9 and Fedora 33. It is now common that Python is upgraded on a similar schedule in every odd-numbered Fedora release.

Note that upstream's "release candidates" are frozen except for blocker bugs. Since we can and will backport blocker fixes between Fedora and upstream, we essentially treat the Release Candidate as the final release.

Notes from the previous upgrade

There are notes from the previous upgrade available, so this upgrade may go smoother: SIGs/Python/UpgradingPython

Benefit to Fedora

Fedora aims to showcase the latest in free and open-source software - we should have the most recent release of Python 3. Packages in Fedora can use the new features from 3.12.

There's also a benefit to the larger Python ecosystem: by building Fedora's packages against 3.12 while it's still in development, we can catch critical bugs before the final 3.12.0 release.

Scope

We will coordinate the work in a side tag and merge when ready.

• Proposal owners:
  1. Introduce python3.12 for all Fedoras
  2. Prepare stuff in Copr as explained in description.
  3. Update python-rpm-macros so python3.12 builds python3
  4. Build python3.12 as the main Python
  5. Mass rebuild all the packages that runtime require python(abi) = 3.11 and/or libpython3.11.so.1.0 (~3900 known packages in October 2022)
  6. Build python3.12 as a non-main Python

• Other developers: Maintainers of packages that fail to rebuild during the rebuilds will be asked, using e-mail and bugzilla, to fix or remove their packages from the distribution. If any issues appear, they should be solvable either by communicating with the respective upstreams first and/or applying downstream patches. Also, the package maintainers should have a look at: Porting to Python 3.12. The python-maint team will be available to help with fixing issues.

• Release engineering: [TBD] A targeted rebuild for all python packages will be required, before the mass rebuild.
  • List of deliverables: nope

• Policies and guidelines: nope

• Trademark approval: nope

Upgrade/compatibility impact

All the packages that depend on Python 3 must be rebuilt. User written Python 3 scripts/applications may require a small amount of porting, but mostly Python 3.11 is forward compatible with Python 3.12.

The Python standard library distutils module will be removed

For many years distutils module was providing support for building and installing additional modules into a Python installation. Since Python 3.10 distutils package is deprecated, and will be removed in Python 3.12. Its functionality for specifying package builds has already been completely replaced by third-party packages setuptools and packaging, and most other commonly used APIs are available elsewhere in the standard library (such as platform, shutil, subprocess or sysconfig).

Affected packages will be failing with ModuleNotFoundError: No module named 'distutils'.

The python3-setutpools package provides a distutils module, so sometimes "simply" adding BuildRequires: python3-setuptools might workaround the problem. Unfortunately, it is not 100 % compatible with the removed standard library one distutils: https://github.com/pypa/setuptools/issues/3532

Fedora packagers can check if their packages build without distutils by removing it form Python 3.11:

1. fedpkg clone <package name> && cd <package name>
2. mock -r fedora-rawhide-x86_64 init
3. mock -r fedora-rawhide-x86_64 install python3-devel
4. sudo rm -rf /var/lib/mock/fedora-rawhide-x86_64/root/usr/lib64/python3.11/distutils/
5. fedpkg mockbuild -N

Later, when Python 3.12 COPR is available, you can use it for testing.

See https://lists.fedoraproject.org/archives/list/python-devel@lists.fedoraproject.org/thread/N6ITYHLRWIDNYNXGPYG2ZHF3ZLQWZN7L/ for known Fedora packages that'll need changes.

pathfix.py tool will be removed

Since Python 2.0 (1994), Python provided a useful tool pathfix.py that we use in Python RPM macros for fixing shebangs of Python modules and some RPM packages use it as well directly in their specfiles for similar purposes. The script will no longer be part of CPython source code and python3-devel RPM package. Because we think it's useful, we have decided to create a new upstream project for it on Github and include it in the python3-rpm-macros package. The change means the script will move from /usr/bin/pathfix.py to /usr/lib/rpm/redhat/pathfix.py. The script will no longer be executable and it will need to be invoked via %{python3} or /usr/bin/python3.

For users of %py_shebang_fix and %py3_shebang_fix no action is needed. The macros will soon use the new location of the tool.

If you use the tool directly in your specfile a change is needed before Python 3.12 become the main one in Fedora 38. We have a list of affected packages and will open PRs for them soon. The list is also a part of the aforementioned PR for python-rpm-macros.

See https://lists.fedoraproject.org/archives/list/python-devel@lists.fedoraproject.org/thread/XPWKHEJHWCJSOHKA6RZG3UYBJIKU6HB3/

How To Test

Interested testers do not need special hardware. If you have a favourite Python 3 script, module, or application, please test it with Python 3.12 and verify that it still works as you would expect. If the application you are testing does not require any other modules, you can test it using python3.12 even before this change is implemented, in Fedora 36, 37 or 38.

In case your application requires other modules, or if you are testing an rpm package, it is necessary to install the 3.12 version of the python3 rpm. Right now that rpm is available in copr, along with all other python packages that build successfully with python 3.12. See https://copr.fedorainfracloud.org/coprs/g/python/python3.12/ for detailed instructions on how to enable Python 3.12 copr for mock.

Once the change is in place, test if your favourite Python apps are working as they were before. File bugs if they don't.

User Experience

Regular distro users shouldn't notice any change in system behaviour other than the Python 3 interpreter will be in version 3.12.

Dependencies

4000+ packages depend on Python 3 and ~3900 packages need rebuilding when Python is upgraded. See scope section.

Contingency Plan

• Contingency mechanism: Do not merge the side tag with rawhide. If the side tag has been merged and issues arise, that will justify a downgrade, then use an epoch tag to revert to 3.11 version (never needed before)
• Contingency deadline: TBD
• Blocks release? Yes, we'd like to block Fedora 39 release on at least 3.12.0rc1
• Blocks product? See above

Documentation

Python 3.12 Release Schedule

Features for 3.12

What's new in 3.12

Porting to Python 3.12

Release Notes

• Migrating user installed packages - https://pagure.io/fedora-docs/release-notes/issue/503