Pytest-Python 2.7 and 3.4 support

It is demanding on the maintainers of an open source project to support
many Python versions, as there’s extra cost of keeping code compatible
between all versions, while holding back on features only made possible
on newer Python versions.

In case of Python 2 and 3, the difference between the languages makes it
even more prominent, because many new Python 3 features cannot be used
in a Python 2/3 compatible code base.

Python 2.7 EOL has been reached in
2020
, with the last
release made in April, 2020.

Python 3.4 EOL has been reached in
2019
, with
the last release made in March, 2019.

For those reasons, in Jun 2019 it was decided that pytest 4.6 series
will be the last to support Python 2.7 and 3.4.

What this means for general users

Thanks to the
python_requires
setuptools option, Python 2.7 and Python 3.4 users using a modern pip
version will install the last pytest 4.6.X version automatically even if
5.0 or later versions are available on PyPI.

Users should ensure they are using the latest pip and setuptools
versions for this to work.

Maintenance of 4.6.X versions

Until January 2020, the pytest core team ported many bug-fixes from the
main release into the 4.6.x branch, with several 4.6.X releases being
made along the year.

From now on, the core team will no longer actively backport patches,
but the 4.6.x branch will continue to exist so the community itself
can contribute patches.

The core team will be happy to accept those patches, and make new 4.6.X
releases until mid-2020 (but consider that date as a ballpark, after
that date the team might still decide to make new releases for critical
bugs).

Technical aspects

(This section is a transcript from
#5275).

In this section we describe the technical aspects of the Python 2.7 and
3.4 support plan.

What goes into 4.6.X releases

New 4.6.X releases will contain bug fixes only.

When will 4.6.X releases happen

New 4.6.X releases will happen after we have a few bugs in place to
release, or if a few weeks have passed (say a single bug has been fixed
a month after the latest 4.6.X release).

No hard rules here, just ballpark.

Who will handle applying bug fixes

We core maintainers expect that people still using Python 2.7/3.4 and
being affected by bugs to step up and provide patches and/or port bug
fixes from the active branches.

We will be happy to guide users interested in doing so, so please don’t
hesitate to ask.

Backporting changes into 4.6

Please follow these instructions:

  1. git fetch --all --prune

  2. git checkout origin/4.6.x -b backport-XXXX # use the PR number
    here

  3. Locate the merge commit on the PR, in the merged message, for
    example:

    nicoddemus merged commit 0f8b462 into pytest-dev:features

  4. git cherry-pick -m1 REVISION # use the revision you found above
    (0f8b462).

  5. Open a PR targeting 4.6.x:

    • Prefix the message with [4.6] so it is an obvious backport
    • Delete the PR body, it usually contains a duplicate commit
      message.

Providing new PRs to 4.6

Fresh pull requests to 4.6.x will be accepted provided that the
equivalent code in the active branches does not contain that bug (for
example, a bug is specific to Python 2 only).

Bug fixes that also happen in the mainstream version should be first
fixed there, and then backported as per instructions above.

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