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GH-132439: Fix REPL swallowing characters entered with AltGr on cmd.exe#132440

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ambv merged 13 commits into
python:mainfrom
chris-eibl:fix_altgr
May 5, 2025
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GH-132439: Fix REPL swallowing characters entered with AltGr on cmd.exe#132440
ambv merged 13 commits into
python:mainfrom
chris-eibl:fix_altgr

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@chris-eibl

@chris-eibl chris-eibl commented Apr 12, 2025 •
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E.g. on my keyboard with German layout, { is usually entered via pressing the AltGr key and 7, i.e. AltGr+7.

Likewise, }, [, ], \ and some more can only be entered via AltGr.

But since #128388 / #128389 these are swallowed by the REPL on Windows and can no longer be entered.

This happens in legacy Windows terminals, where the virtual terminal mode is turned off (e.g. cmd.exe).

In virtual terminal mode there are other issues, see #131878.

@bedevere-app bedevere-app Bot mentioned this pull request Apr 12, 2025
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@chris-eibl chris-eibl added OS-windows 3.13 bugs and security fixes 3.14 topic-repl Related to the interactive shell labels Apr 12, 2025
@chris-eibl chris-eibl requested a review from vstinner April 12, 2025 14:49
@chris-eibl

chris-eibl commented Apr 12, 2025

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Adding @vstinner, @eendebakpt and @paulie4 , since they were involved in #128389 and already talked about AltGr.

@chris-eibl

chris-eibl commented Apr 12, 2025

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PS: switching to an english keyboard layout, I can use the AltGr key like right-Alt, since it is not used in this keyboard layout :)

@picnixz picnixz added needs backport to 3.13 and removed 3.13 bugs and security fixes 3.14 bugs and security fixes labels Apr 12, 2025
@chris-eibl

chris-eibl commented Apr 12, 2025

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The failing of Ubuntu (free-threading) is definitely unrelated, since this is a Windows specific change.

@tomasr8

tomasr8 commented Apr 17, 2025

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Do you think it'd be possible to add some tests for this change to ensure we don't accidentally regress again?

@chris-eibl

chris-eibl commented Apr 17, 2025

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Yeah, I've already thought about it, but am still unsure how to best do it.

ATM, I am thinking of mocking

cpython/Lib/_pyrepl/windows_console.py

Line 411 in b87189d

def _read_input(self, block: bool = True) -> INPUT_RECORD | None:

to be able to test

cpython/Lib/_pyrepl/windows_console.py

Lines 426 to 432 in b87189d

def get_event(self, block: bool = True) -> Event | None:
"""Return an Event instance. Returns None if |block| is false
and there is no event pending, otherwise waits for the
completion of an event."""
while self.event_queue.empty():
rec = self._read_input(block)

AFAICT, all the existing tests just mock get_event, but for this, IMHO get_event itself must be tested.
Mocking _read_input seems to be the best way forward.

WDYT?

@tomasr8

tomasr8 commented Apr 17, 2025

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Agreed that we shouldn't be mocking get_event since that's where we're making changes. _read_input seems like a good option, we can capture some real inputs and then replay them with it.

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This was referenced Apr 24, 2025
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@ambv ambv changed the title GH-132439: REPL on Windows swallows characters entered via AltGr May 5, 2025
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ambv approved these changes May 5, 2025
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Excellent work again! Very well thought through.

@ambv ambv merged commit 07f416a into python:main May 5, 2025
@miss-islington-app

miss-islington-app Bot commented May 5, 2025

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Thanks @chris-eibl for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

@miss-islington-app

miss-islington-app Bot commented May 5, 2025

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Sorry, @chris-eibl and @ambv, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 07f416a3f063db6b91b8b99ff61a51b64b0503f1 3.13

@ambv ambv changed the title GH-132439: Fix REPL swallowing characters entered with AltGr May 5, 2025
@sergey-miryanov

sergey-miryanov commented May 5, 2025

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Will repeat here too - problem with backport because VT support was not backported #130805 (comment) (for completeness)

@ambv

ambv commented May 5, 2025

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Yeah, I am backporting the VT support too because it's the only way we can have a sensibly similar codebase for bug fixes.

ambv pushed a commit to ambv/cpython that referenced this pull request May 5, 2025
@chris-eibl @StanFromIreland @ambv
[3.13] pythonGH-132439: Fix REPL swallowing characters entered with A… …
3662540 
…ltGr on cmd.exe (pythonGH-132440)

(cherry picked from commit 07f416a)

Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
@bedevere-app

bedevere-app Bot commented May 5, 2025

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GH-133460 is a backport of this pull request to the 3.13 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.13 bugs and security fixes label May 5, 2025
ambv added a commit that referenced this pull request May 5, 2025
@ambv @chris-eibl @StanFromIreland
[3.13] GH-132439: Fix REPL swallowing characters entered with AltGr o… …
e4d6848 
…n cmd.exe (GH-132440) (GH-133460)

(cherry picked from commit 07f416a)

Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
@chris-eibl chris-eibl deleted the fix_altgr branch May 5, 2025 18:14
@eendebakpt eendebakpt mentioned this pull request Jun 3, 2025
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Pranjal095 pushed a commit to Pranjal095/cpython that referenced this pull request Jul 12, 2025
@chris-eibl @StanFromIreland @Pranjal095
pythonGH-132439: Fix REPL swallowing characters entered with AltGr on… …
bace14d 
… cmd.exe (pythonGH-132440)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
@chris-eibl chris-eibl mentioned this pull request Mar 13, 2026
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