Revision as of 14:34, 17 April 2019

Retire Python 2 (and let it all burn)

Summary

The python2 package and all it's subpackages will be removed from Fedora 32. A legacy python27 package for developers and users will be provided. All packages in Fedora that need Python 2 to run will be removed from Fedora 32 regardless of their dependencies. All packages in Fedora that need Python 2 to build will be removed from Fedora 32 regardless of their dependencies. Exceptions can be granted by FESCo.

Owner

Name: Miro Hrončok
Email: <mhroncok@redhat.com> <python-devel@lists.fedoraproject.org>
Release notes owner:

Current status

Targeted release: Fedora 32
Last updated: 2019-04-17
Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Python 2 is unsupported upstream since 2020-01-01. After two phased approaches to limit the dependent packages on Python 2:

The Python maintenance team has decided to pull the plug. The python2 package and all it' subpackages will be retired (read: removed) from Fedora 32 (Rawhide) as soon as Fedora 31 is branched.

All packages depending on any python2 package will be removed. The removal starts 2 week before the planned Fedora 32 Mass Rebuild. Broken dependencies will not stop the removals. Packages that Fail to Build From Source and prevent to remove Python 2 subpackages may end up with broken dependencies, in cases where it is not desired, those packages will be retired instead.

The rules also apply to modules built for Fedora 32+.

The packages removal will be executed in an automated fashion.

Removed packages that would otherwise block the upgrades to Fedora 32 will be obsoleted from fedora-obsolete-packages.

The python27 package

Similarly to existing python36, python37 etc. packages, a python27 package will be created. This package is indented for Python developers who still need to support the legacy version of Python. This package is indented for users, who still need to use some software depending on the legacy version of Python. This package is not intended for other Fedora packages to be dependent upon.

The python27 package has several drawbacks compared to the original python2 package:

it is "flat" - there are no subpackages, everything lives in one package
there is no debug build (previously available as python2-debug)
there is no /usr/bin/python (note: there might be already the case before this change)
any special backwards compatible provides are removed (this package is not intended to be dependent upon)

FESCo exceptions

We realize that there are some packages whose removal could seriously hurt Fedora. FESCo can grant exceptions for packages to use the python27 as a runtime or build dependency.

The package maintainer is responsible to check the entire dependency chain and they need to request exception for the entire list of packages. For example, when seeking exception for the chromium package, it should contain python-psutil and other dependent packages. Yes, this is tedious. Maintaining a Python 2 dependent package is a burden. A Python 3 plan is a must for such exception.

Any non-essential dependency must be dropped. That includes optional dependencies, test dependencies, optional subpackages etc.

Package that fail to get an exception when the removal starts (see above) will be removed. Their importance for Fedora Release Engineering, Fedora Infrastructure or any other body will not be automagically respected, every package that needs Python 2 needs an exception.

The change owners will send regular reminders to the package owners.

Benefit to Fedora

Python 2 is past upstream End of Life since 2020-01-01. This changes is generally crafted in a way that:

it leaves Python developers an option to use it in case they still need to support it
it leaves Fedora users an option to use it in case they still need it to run their (3rd party) software
it leaves Fedora packagers an option to keep using it, arguably complicated but possible

While:

it removes Python 2 software from Fedora that was only preserved so far by inaction

Using Python 2 is dangerous. While the Fedora Python maintainers will try to fix as much security bugs as possible, without the upstream involvement, this will not always be possible. This change moves Python 2 from second class citizen to third class citizen. Python 2 was deprecated since Fedora 30.

Scope

Proposal owners:
- retire python2
- introduce python27
- remove all python2 dependent packages without exceptions
- obsolete removed packages that break the upgrade path via fedora-obsolete-packages

Other developers:
- remove their python2 dependent packages without exceptions
- get exceptions if needed
- fix broken dependencies

Release engineering: #Releng issue number (a check of an impact with Release Engineering is needed)
- List of deliverables: none

Policies and guidelines: Python 2 packaging is against the guidelines since Fedora 30. Python 2 packaging guidelines will be removed from Python Appendix.

Trademark approval: not needed for this Change

Upgrade/compatibility impact

Majority of removed packages will be obsoleted and removed on upgrade.

Users needing Python 2 libraries will need to use pip and virtualenv.

How To Test

Try to update Fedora 30 or 31 to 32. No python2 packages should block the upgrade. Try to run Python 2 software via the python27 package.

User Experience

There will be close to zero Python 2 RPMs in Fedora repos. Users are encouraged to switch to Python 3 and/or use Python 2 virtual environments and pip for development.

Dependencies

N/A (not a System Wide Change)

Contingency Plan

Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
Contingency deadline: N/A (not a System Wide Change)
Blocks release? N/A (not a System Wide Change), Yes/No
Blocks product? product

Documentation