Gentoo Archives: gentoo-dev

From: "Michał Górny" <mgorny@g.o>
To: gentoo-dev@l.g.o
Subject: Re: [gentoo-dev] [News item review v2] Python preference to follow PYTHON_TARGETS
Date: Sun, 24 Jan 2021 12:59:10
Message-Id: adca910cd6703a2095fd03744dbee41bb165f521.camel@gentoo.org
In Reply to: [gentoo-dev] [News item review] Python preference to follow PYTHON_TARGETS by "Michał Górny"
1 Here's v2 with extra 'tl;dr' instructions in first para:
2
3 ```
4 Title: Python preference to follow PYTHON_TARGETS
5 Author: Michał Górny <mgorny@g.o>
6 Posted: 2021-01-24
7 Revision: 1
8 News-Item-Format: 2.0
9
10 On 2021-02-01 stable users will switch to a new method of updating
11 the preferred Python versions that employs the configuration update
12 mechanism in order to follow PYTHON_TARGETS. We will also deprecate
13 and stop installing app-eselect/eselect-python by default. If you wish
14 to use the newest Python version present in your PYTHON_TARGETS, you
15 only have to accept configuration changes. If you wish need
16 to customize the behavior, read on.
17
18 Since 2017, /usr/bin/python and the related non-versioned symlinks
19 are wrapped through dev-lang/python-exec. The list of preferred Python
20 implementations is stored in /etc/python-exec/python-exec.conf and/or
21 per-program /etc/python-exec/<basename>.conf configuration files.
22 To preserve backwards compatibility, app-eselect/eselect-python remained
23 a wrapper that updated this file.
24
25 However, this mechanism alone has proven inconvenient to end users who
26 had to update python-exec.conf whenever the default PYTHON_TARGETS
27 changed. Thanks to the fallback logic, this was not a major problem
28 for software installed via Gentoo packages that always ensure that
29 a supported implementation is used. However, users have reported that
30 whenever the preference for /usr/bin/python mismatched their
31 PYTHON_TARGETS, their custom scripts would break due to unsatisfied
32 dependencies. This does not follow the principle of least surprise.
33
34 For this reason, we have decided to change the default python-exec
35 configuration to match PYTHON_TARGETS by default, in the eclass
36 preference order, that is from the newest CPython version to oldest,
37 with alternative Python implementations coming afterwards. This change
38 will be propagated via the configuration protection mechanism whenever
39 dev-lang/python-exec-conf is installed or rebuilt due to PYTHON_TARGETS
40 changes. This will permit the users to interactively confirm
41 the updates.
42
43 If the new default is not correct for you, please use your preferred
44 configuration update tool to discard or edit the new configuration file.
45
46 Furthermore, dev-lang/python will no longer attempt to automatically
47 update the Python interpreter preference, or pull in eselect-python
48 automatically. If you wish to continue using it, please install it
49 manually to ensure that it is not unmerged.
50
51 ```
52
53 --
54 Best regards,
55 Michał Górny

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