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gh-139551: add support for BaseExceptionGroup in IDLE#139563

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gpshead merged 15 commits intopython:mainfrom
Locked-chess-official:baseexceptiongroupsupport
Apr 12, 2026
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gh-139551: add support for BaseExceptionGroup in IDLE#139563
gpshead merged 15 commits intopython:mainfrom
Locked-chess-official:baseexceptiongroupsupport

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@Locked-chess-official Locked-chess-official commented Oct 4, 2025 •
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Locked-chess-official commented Oct 4, 2025 •
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Now I have found one different between the IDLE and REPL in this change. However, I don't think it affects:
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Locked-chess-official commented Oct 5, 2025

The change that if isinstance(val, BaseExceptionGroup) branch becomes a function alone is difficult because it is a closure function.

@picnixz picnixz changed the title gh-139551: add the support for BaseExceptionGroup gh-139551: support for BaseExceptionGroup in IDLE Oct 5, 2025
@picnixz picnixz changed the title gh-139551: support for BaseExceptionGroup in IDLE gh-139551: add support for BaseExceptionGroup in IDLE Oct 5, 2025
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Can you add tests and a What's New entry as well? I think the code could also avoid having all those if prefix: inside the for loops and many times, the additional string is either two spaces or the given prefix.

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Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
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picnixz commented Oct 5, 2025

More generally, don't we have a helper in traceback for rendering exception groups actually? Can't we use it?

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Locked-chess-official commented Oct 5, 2025 •
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More generally, don't we have a helper in traceback for rendering exception groups actually? Can't we use it?

Maybe not. In IDLE, it need traceback.print_list to print the right tb. If we use it, one tb with file "<pyshell#x>" will have no code and there will be a tb exec(code). So the code must be writed alone here.

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picnixz commented Oct 5, 2025

Ok. For now, let's write it as is, and later we can rewrite the exception rendering logic by using the same approach as for traceback.TracebackException where we use a context for indentation. It could reduce the code complexity (compare the current code with traceback.TracebackException.format)

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Locked-chess-official commented Oct 5, 2025

I have no idea whether to do it. What should be used is traceback._ExceptionPrintContext wich is a private attribute.

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picnixz commented Oct 5, 2025

No, I meant, we should mimic this ourselves. We may need to tweak the context itself, but the approach can be taken. Not in this PR though I would say as it may be too much changes in one PR.

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CoolCat467 commented Apr 12, 2026

I encounter exactly this issue all the time, sorry to bother again but @gpshead could you look at this as well whenever you have time?

gpshead and others added 5 commits April 11, 2026 23:58
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Merge branch 'main' into baseexceptiongroupsupport
1010bca
@gpshead @claude
Fix missing file=efile in IDLE's ExceptionGroup cycle-detection output
16abdaf 
The print call for the "exception has printed" message in
print_exc_group was writing to stdout instead of stderr.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
@gpshead @claude
Replace boolean multiplication with explicit 'and' in print_exc_group
4ea0d84 
The expression need_print_underline *= (i == len(exc.exceptions))
used bool*bool as a substitute for logical and. Replace with a
readable conditional.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
@gpshead @claude
Add tests for BaseExceptionGroup rendering in IDLE's print_exception
576b223 
Test nested groups, __cause__/__context__ chaining inside groups,
and cycle detection for the exception group display code.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
@gpshead @claude
Add max_group_width and max_group_depth limits to IDLE's ExceptionGro…
990213c 
…up rendering

Match the traceback module defaults (max_group_width=15,
max_group_depth=10) to prevent pathological exception groups from
producing unbounded output or stack overflow via recursion.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
@gpshead gpshead self-assigned this Apr 12, 2026
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I polished things a little & added tests, this should be ready, it appears to work as expected.

pie in the sky: I do wish idle didn't reinvent its own exception rendering and could just use the traceback module - but if it even makes sense to do that (it may not), it'd be an entirely different cleanup.

@gpshead gpshead merged commit 1e79bf6 into python:main Apr 12, 2026
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