GH-133711: Enable UTF-8 mode by default (PEP 686) by AA-Turner · Pull Request #133712 · python/cpython

AA-Turner · 2025-05-08T21:21:32Z

Issue: Enable UTF-8 mode by default (implement PEP 686) #133711

📚 Documentation preview 📚: https://cpython-previews--133712.org.readthedocs.build/

zooba · 2025-05-09T10:19:05Z

+* Python UTF-8 mode is now enabled by default.
+ It may be disabled with by setting :envvar:`PYTHONUTF8=0 <PYTHONUTF8>` as
+ an environment variable or by using the :option:`-X utf8=0 <-X>` flag.
+ See :pep:`686` for further details.


I feel like we can probably put some more explanation in here, such as that it affects TextIOWrapper and hence open(). The current description doesn't sound as scary as it needs to, in my opinion.
Along the lines of: "Python UTF-8 mode is now enabled by default. This means that (files/console/etc.) will now use UTF-8 regardless of system settings, unless specifically overridden in code (typically with an encoding= argument)."

To be clear, it's nothing new. But we shouldn't assume that everyone already knows what UTF-8 mode implies. There are many more people out there who haven't ever thought about it than those who are waiting for it to be the default.

Another effect of the UTF-8 Mode is that Python ignores the locale encoding.

I've expanded the What's New entry, please see https://cpython-previews--133712.org.readthedocs.build/en/133712/whatsnew/3.15.html#other-language-changes

vstinner · 2025-05-10T07:25:22Z

 ======================

-
+* Python now uses UTF-8_ as the default encoding, independent of the system's


You might mention the UTF-8 Mode earlier since it has other side effects documented in the UTF-8 Mode section, such as changing sys.stdout error handler and ignoring the locale encoding.

"default encoding" is UTF-8 since Python 3.0. (e.g. sys.getdefaultencoding())

# Conflicts: # Doc/whatsnew/3.15.rst

vstinner · 2025-05-28T14:50:55Z

test_regrtest failed:

I wrote #134839 to fix test_regrtest when PYTHONUTF8=1 env var is set.

vstinner · 2025-05-28T15:25:01Z

I can also reproduce the [test_readline] issue in the main branch using the fr_FR locale and the command:
PYTHONUTF8=1 LANG=fr_FR ./python -m test -v test_readline -u all

I wrote #134841 to fix test_readline for the Python UTF-8 Mode.

vstinner · 2025-05-28T16:31:58Z

buildbot/wasm32-wasi Non-Debug PR — Build done.

Configure host Python fails with:

checking for /dev/ptmx... not set
configure: error: set ac_cv_file__dev_ptmx to yes/no in your CONFIG_SITE file when cross compiling

It seems to be unrelated to this PR.

AA-Turner · 2025-05-29T16:52:07Z

buildbot/wasm32-wasi Non-Debug PR — Build done.
Configure host Python fails with:
checking for /dev/ptmx... not set
configure: error: set ac_cv_file__dev_ptmx to yes/no in your CONFIG_SITE file when cross compiling
It seems to be unrelated to this PR.

cc @brettcannon, this builder seems to be consistently failing since ~15/05.

vstinner

LGTM.

vstinner · 2025-06-16T14:17:05Z

Ping @AA-Turner, I made two suggestions.

vstinner · 2025-07-13T17:06:01Z

vstinner disabled auto-merge

In fact, it would be safe to run this PR on buildbots before merging it. I will wait until GitHub CIs complete first.

bedevere-bot · 2025-07-13T18:32:32Z

🤖 New build scheduled with the buildbot fleet by @vstinner for commit 3130318 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F133712%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

AA-Turner · 2025-07-15T09:45:28Z

Thanks @vstinner!

A

Co-authored-by: Victor Stinner <vstinner@python.org>

Enable UTF-8 mode by default (PEP 686)
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AA-Turner requested a review from methane May 8, 2025 21:21

AA-Turner requested review from FFY00, ericsnowcurrently and gpshead as code owners May 8, 2025 21:21

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Enable UTF-8 mode by default (implement PEP 686) #133711
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AA-Turner added 3 commits May 10, 2025 01:47

Victor's documentation comments
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Fix test_cmd_line
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Improve What's New entry
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Add references to UTF-8 and Unicode
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Merge branch 'main' into utf-8-mode
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Check stream buffer type in test_python_legacy_windows_stdio
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Merge branch 'main' into utf-8-mode
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# Conflicts: # Doc/whatsnew/3.15.rst

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Merge branch 'main' into utf-8-mode
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Update Doc/library/os.rst
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Update Include/cpython/initconfig.h
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Merge branch 'main' into utf-8-mode
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AA-Turner merged commit c89a66f into python:mainJul 15, 2025
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taegyunkim pushed a commit to taegyunkim/cpython that referenced this pull request Aug 4, 2025
pythonGH-133711: Enable UTF-8 mode by default (PEP 686) (python#133712)
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Co-authored-by: Victor Stinner <vstinner@python.org>

Agent-Hellboy pushed a commit to Agent-Hellboy/cpython that referenced this pull request Aug 19, 2025
pythonGH-133711: Enable UTF-8 mode by default (PEP 686) (python#133712)
e7da33e
Co-authored-by: Victor Stinner <vstinner@python.org>

coderabbitaiBot mentioned this pull request May 6, 2026
Implement agent tool management CLI leynos/repo-local-tools#6
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		======================


		* Python now uses UTF-8_ as the default encoding, independent of the system's

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