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GeezerVison is showing github.com — gh-149083: Use sentinel for os.path.{ALLOW_MISSING,ALL_BUT_LAST} by JelleZijlstra · Pull Request #149613 · python/cpython

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@JelleZijlstra

@JelleZijlstra JelleZijlstra commented May 9, 2026 •
edited by bedevere-app Bot
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ALL_BUT_LAST is new in 3.15 (#117562). ALLOW_MISSING is also recent (#135037) but was backported to other branches for security reasons.

Making these sentinels has a few effects:

  • The repr changes from os.path.ALLOW_MISSING to just ALLOW_MISSING
  • The docstring is no longer present on the object itself.

Still it seems worth it to simplify to standard sentinels for 3.15+.

  • Issue: Use PEP 661 (sentinels) in the standard library #149083

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@JelleZijlstra JelleZijlstra added the needs backport to 3.15 bugs and security fixes label May 9, 2026
@bedevere-app bedevere-app Bot mentioned this pull request May 9, 2026
Use PEP 661 (sentinels) in the standard library #149083
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@bedevere-app bedevere-app Bot added the awaiting core review label May 9, 2026
@read-the-docs-community

read-the-docs-community Bot commented May 9, 2026 •
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Documentation build overview

📚 cpython-previews | 🛠️ Build #32618158 | 📁 Comparing 71b5fee against main (7241f27)

  🔍 Preview build  

2 files changed
± library/os.path.html
± whatsnew/changelog.html
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serhiy-storchaka
serhiy-storchaka reviewed May 9, 2026
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Comment thread Lib/genericpath.py Outdated
return self.__class__.__name__
# Sentinels.
ALL_BUT_LAST = sentinel('ALL_BUT_LAST')
"""Special value for use in realpath()."""

@serhiy-storchaka serhiy-storchaka May 9, 2026

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Is it used as a docstring of the sentinel? I wonder, how can this be implemented?

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@JelleZijlstra JelleZijlstra May 9, 2026

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Sentinels don't actually support docstrings. Putting a string like this is an established way to document a variable and I believe Sphinx supports it.

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@serhiy-storchaka serhiy-storchaka May 9, 2026

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Then they are not needed.

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@JelleZijlstra JelleZijlstra closed this May 17, 2026
@JelleZijlstra
JelleZijlstra force-pushed the main branch from 71b5fee to acefff9 Compare May 17, 2026 22:54
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@JelleZijlstra @serhiy-storchaka
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