[gentoo-dev] News item review: Python 3.7 to become the default target

[Michał Górny]

Hi,

It's finally time to move away from 3.6.  The news item is roughly based
on the one for 3.6, with some grammar fixes and removal of the EOL part.

Please also note that this is the *last* call to port packages to Python
3.7 *and* 3.8.  Python 3.6 is no longer receiving bugfixes for a long
time now, and 3.7 will stop receiving them in June.  That's how far
behind we are.  I would personally prefer going straight to 3.8 if that
was realistically possible in less than 2 years.

---

Title: Python 3.7 to become the default target
Author: Michał Górny <mgorny@g.o>
Posted: 2020-04-19
Revision: 1
News-Item-Format: 2.0
Display-If-Installed: dev-lang/python:3.6

On 2020-05-04, Python 3.7 will replace Python 3.6 as one of the default
Python target for Gentoo systems.  The new default targets will be:

    PYTHON_TARGETS="python2_7 python3_7"
    PYTHON_SINGLE_TARGET="python3_7"

If you have not overriden the value of those variables on your system,
then your package manager will switch to the new targets immediately.
In order to prevent dependency conflicts, please clean stray packages
and rebuild/upgrade all packages with USE flag changes after the change,
e.g.:

    emerge --depclean
    emerge -1vUD @world
    emerge --depclean

Please note that upgrading dependencies in place may cause some
of the package dependencies to be temporarily missing.  While this
should not affect scripts that are already fully loaded, it may cause
ImportErrors while starting Python scripts or loading additional
modules (only scripts running Python 3.6 are affected).

In order to improve stability of the upgrade, you may choose to
temporarily enable both targets, i.e. set in /etc/portage/make.conf
or its equivalent:

    PYTHON_TARGETS="python2_7 python3_6 python3_7"
    PYTHON_SINGLE_TARGET="python3_6"

This will cause the dependencies to include both Python 3.6 and 3.7
support on the next system upgrade.  Once all packages are updated,
you can restart your scripts, remove the custom setting and run another
upgrade to remove support for Python 3.6.

If you would like to postpone the switch to Python 3.7, you can copy
the current value of PYTHON_TARGETS and/or PYTHON_SINGLE_TARGET
to /etc/portage/make.conf or its equivalent:

    PYTHON_TARGETS="python2_7 python3_6"
    PYTHON_SINGLE_TARGET="python3_6"

If you would like to migrate your systems earlier, you can do the same
with the new value.

Please note that the switch is long overdue.  Python 3.6 is no longer
receiving bug fixes.  Its planned end-of-life is 2021-12-23 but we will
probably remove it earlier than that.  [1]

[1]:https://devguide.python.org/#status-of-python-branches


-- 
Best regards,
Michał Górny