Signed-off-by: Michał Górny <mgo...@gentoo.org> --- .../2021-04-29-python3-9.en.txt | 119 ++++++++++++++++++ 1 file changed, 119 insertions(+) create mode 100644 2021-04-29-python3-9/2021-04-29-python3-9.en.txt
diff --git a/2021-04-29-python3-9/2021-04-29-python3-9.en.txt b/2021-04-29-python3-9/2021-04-29-python3-9.en.txt new file mode 100644 index 0000000..fc55427 --- /dev/null +++ b/2021-04-29-python3-9/2021-04-29-python3-9.en.txt @@ -0,0 +1,119 @@ +Title: Python 3.9 to become the default on 2021-06-01 +Author: Michał Górny <mgo...@gentoo.org> +Posted: 2021-04-29 +Revision: 1 +News-Item-Format: 2.0 +Display-If-Installed: dev-lang/python:3.7 +Display-If-Installed: dev-lang/python:3.8 + +We are planning to switch the default Python target of Gentoo systems +on 2021-06-01, from Python 3.8 to Python 3.9. If you have not changed +the values of PYTHON_TARGETS or PYTHON_SINGLE_TARGET, the change will +have immediate effect on your system and the package manager will try +to switch automatically on the next upgrade following the change. + +If you did change the values, prefer a safer approach or have problems +with the update, read on. + +Please note that the default upgrade method switches packages to the new +Python versions as they are rebuilt. This means that all interdependent +packages have to support the new version for the upgrade to proceed, +and that some programs may temporarily fail to find their dependencies +throughout the upgrade (although programs that are already started +are unlikely to be affected). + + +If you have PYTHON_TARGETS or PYTHON_SINGLE_TARGET declared +in make.conf, please remove these declarations as they will interfere +with the package.use samples provided below. Using make.conf for Python +targets is discouraged as it prevents package defaults from applying +when necessary. This news item assumes using /etc/portage/package.use +or your package manager's equivalent file for configuration. + + +At this point, you have a few configuration options to choose from: + +1. If you wish Python upgrades to apply automatically, you can remove + PYTHON_TARGETS and PYTHON_SINGLE_TARGET declarations. When + the defaults change, your package manager should handle the upgrade + automatically. However, you may still need to run the update + commands if any problems arise. + +2. If you wish to defer the upgrade for the time being, you can + explicitly set the old values in package.use. + +3. If you wish to force the upgrade earlier, you can explicitly set + the new values and run the upgrade commands. + +4. If you wish to use a safer approach (i.e. less likely to temporarily + break packages during the upgrade), you can perform a multi-step + upgrade as outlined below. + +5. Finally, you can use an arbitrary combination of PYTHON_TARGETS + and PYTHON_SINGLE_TARGET. + + +Deferring the upgrade +===================== +To defer the upgrade, explicitly set the old targets: + + */* PYTHON_TARGETS: -* python3_8 + */* PYTHON_SINGLE_TARGET: -* python3_8 + +This will enforce Python 3.8 and block any future updates. However, +please note that this solution will only be suitable for a few more +months and you will eventually need to perform the migration. + + +Forcing the upgrade +=================== +To force the upgrade earlier, explicitly set Python 3.9 targets: + + */* PYTHON_TARGETS: -* python3_9 + */* PYTHON_SINGLE_TARGET: -* python3_9 + +However, it is important to remember to remove this after the defaults +change, as it will interfere with the automatic switch to the next +Python version in the future. + + +Safer upgrade procedure +======================= +A safer approach is to add Python 3.9 support to your system first, +and only then remove Python 3.8. However, note that involves two +rebuilds of all the affected packages, so it will take noticeably +longer. + +First, enable both Python 3.8 and Python 3.9, and then run the upgrade +commands: + + */* PYTHON_TARGETS: -* python3_8 python3_9 + */* PYTHON_SINGLE_TARGET: -* python3_8 + +Then switch PYTHON_SINGLE_TARGET and run a second batch of upgrades: + + */* PYTHON_TARGETS: -* python3_8 python3_9 + */* PYTHON_SINGLE_TARGET: -* python3_9 + +Finally, switch to the final version and upgrade: + + */* PYTHON_TARGETS: -* python3_9 + */* PYTHON_SINGLE_TARGET: -* python3_9 + +You may wish to remove the target overrides after the defaults switch. +Alternatively, you can keep them to block the next automatic upgrade +to Python 3.10, and upgrade manually then. + + +Upgrade commands +================ +The Python 3.8 cleanup requires that Python 3.8 is removed from complete +dependency trees in batch. If some of the installed packages using +an older Python version are not triaged for the upgrade, the package +manager will throw dependency conflicts. This makes it important that +the upgrade is carried via a --deep --changed-use @world upgrade, +as well as that any stray packages are removed prior to it, e.g.: + + emerge --depclean + emerge -1vUD @world + emerge --depclean -- 2.31.1
