Initial implementation of PEP 661 v2 (sentinels) by JelleZijlstra · Pull Request #4 · JelleZijlstra/cpython

JelleZijlstra · 2026-04-17T03:49:15Z

📚 Documentation preview 📚: https://cpython-previews--4.org.readthedocs.build/

JelleZijlstra · 2026-04-17T05:10:46Z

Open questions:

What about __bool__? Lots of discussion on Discourse, I don't care too much but don't want this to derail the feature. This draft implementation says sentinels are always truthy.
Should sentinels be weakrefable?
Should the sentinel class be subclassable? My inclination is no.
Should there be a C API like PySentinel_New? Probably.

Viicos · 2026-04-17T11:14:41Z

Open questions:

Gave thoughts on python/peps#4923 (comment).

…ex types in the ctype module (pythonGH-148485) Co-authored-by: sunmy2019 <59365878+sunmy2019@users.noreply.github.com>

…or (pythonGH-148523)

…python#148685) Doc: fix misplaced pprint entries in What's New 3.15

…hon#148657) The option parsing in Modules/_zstd/decompressor.c had a missing Py_DECREF(value) before the early return -1 when PyLong_AsInt(key) fails. The identical code in Modules/_zstd/compressor.c line 158 has the fix.

…ython#148693)

…ython#148226)

Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com>

) Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com> Co-authored-by: Petr Viktorin <encukou@gmail.com>

…le objects (pythonGH-148698) Forbid marshalling recursive code, slice and frozendict objects which cannot be correctly unmarshalled. Reject invalid marshal data produced by marshalling recursive frozendict objects which was previously incorrectly unmarshalled. Add multiple tests for recursive data structures.

Co-authored-by: Stan Ulbrych <stan@python.org>

…#148689) If _BlocksOutputBuffer_Finish() fails (memory allocation failure), PyBytesWriter_Discard() is called on the writer. Then if _BlocksOutputBuffer_OnError() is called, it calls again PyBytesWriter_Discard() causing a double free. Fix _BlocksOutputBuffer_Finish() by setting buffer->writer to NULL, so _BlocksOutputBuffer_OnError() does nothing instead of calling PyBytesWriter_Discard() again.

DanielNoord

I only looked at the .rst file as my minimal knowledge of C won't help much here. There are a couple of double spaces in some of them, perhaps before merging quickly grep for " " in the diff to remove those :)

…thongh-148698 (pythonGH-148725)

JelleZijlstra · 2026-04-18T12:53:01Z

Thanks for looking! I think the double spaces are mainly between sentences, that's very common in the docs. It doesn't affect rendering.

…Ts (python#148704) Export a few more functions required for external JITs

…s.py (python#143317) Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

…148408) Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

…on#148739)

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>

…note (pythongh-148882)

…ular __wrapped__ (python#148595)

…stuple (python#145125)

…ases (python#143316) The documentation previously stated that Concatenate is only valid when used as the first argument to Callable, but according to PEP 612, it can also be used when instantiating user-defined generic classes with ParamSpec parameters.

…hints()` (python#143758) Do not mention `__annotations__` dictionaries, as this is slightly outdated since 3.14. Rewrite the note about possible exceptions for clarity. Also do not mention imported type aliases, as since 3.12 aliases with the `type` statement do not suffer from this limitation anymore.

…on#148893)

…pythonGH-148302) Improve ABI/feature selection, add new header for it. Add a test that Python headers themselves don't use Py_GIL_DISABLED in abi3t: abi3 and abi3t ought to be the same except the _Py_OPAQUE_PYOBJECT differences. This is done using the GCC-only poison pragma. Co-authored-by: Victor Stinner <vstinner@python.org>

…` on free-threading (python#148908)

…ython#148872)

… string representations of ForwardRef (python#148682) Co-authored-by: Shamil <ashm.tech@proton.me>

…from both `ValueError` and `IndexError` (python#148664) Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> Co-authored-by: Stan Ulbrych <stan@python.org>

… Lines file (python#132632) Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>

pythongh-148886) Avoid racing with the owning thread's refcount operations when immortalizing an interned string: if we don't own it and its refcount isn't merged, intern a copy we own instead. Use atomic stores in _Py_SetImmortalUntracked so concurrent atomic reads are race-free.

Add '+' alternatives to signed_number and signed_real_number grammar rules, mirroring how unary minus is already handled for pattern matching. Unary plus is a no-op on numbers so the value is returned directly without wrapping in a UnaryOp node.

…ntend (pythonGH-148089) * Replaces ad-hoc logic for ending traces with a simple inequality: `fitness < exit_quality` * Fitness starts high and is reduced for branches, backward edges, calls and trace length * Exit quality reflect how good a spot that instruction is to end a trace. Closing a loop is very, specializable instructions are very low and the others in between.

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Improve `hash()` builtin docstring with caveats. Mention its return type and that the value can be expected to change between processes (hash randomization). Why? The `hash` builtin gets reached for and used by a lot of people whether it is the right tool or not. IDEs surface docstrings and people use pydoc and `help(hash)`.

Fixes python#108951 Co-authored-by: sobolevn <mail@sobolevn.me> Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com> Co-authored-by: Guido van Rossum <guido@python.org>

Initial implementation of PEP 661 v2 (sentinels)

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Viicos reviewed Apr 17, 2026

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Comment thread Objects/sentinelobject.c

Comment thread Objects/sentinelobject.c Outdated

Comment thread Doc/library/functions.rst Outdated

Comment thread Doc/library/functions.rst

Comment thread Doc/library/functions.rst Outdated

Viicos mentioned this pull request Apr 17, 2026

PEP 661: Update python/peps#4923

Merged

skirpichev and others added 17 commits April 17, 2026 14:09

pythongh-148464: Add missing __ctype_le/be__ attributes for compl…

769cc83

…ex types in the ctype module (pythonGH-148485) Co-authored-by: sunmy2019 <59365878+sunmy2019@users.noreply.github.com>

pythongh-148484: Fix memory leak of iterator in array.array construct…

afde756

…or (pythonGH-148523)

pythongh-148683: Doc: fix misplaced pprint entries in What's New 3.15 (…

a86234e

…python#148685) Doc: fix misplaced pprint entries in What's New 3.15

pythongh-146393: Remove special character in optimizer_bytecodes.c (p…

db3e990

…ython#148693)

pythongh-148222: Fix NULL dereference bugs in genericaliasobject.c (p…

634568d

…ython#148226)

Update Doc/library/functions.rst

ededfb7

Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com>

Update Doc/library/functions.rst

39f364c

Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com>

pythongh-148639: Implement PEP 800 (typing.disjoint_base) (python#148640

92164dc

) Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com> Co-authored-by: Petr Viktorin <encukou@gmail.com>

gc, name

0adf314

C API

e4a106a

not needed

e5b8789

use it for NoExtraItems

bdcb400

tweaks

cc4545c

Add a new Sphinx soft-deprecated directive (python#148630)

e9bbf86

Co-authored-by: Stan Ulbrych <stan@python.org>

DanielNoord reviewed Apr 18, 2026

View reviewed changes

pythongh-148653: Fix reference leaks in test_marshal introduced in py…

7ce737e

…thongh-148698 (pythonGH-148725)

JelleZijlstra and others added 5 commits April 18, 2026 05:54

fix warning?

be58215

pythongh-148659: Export a few more functions required for external JI…

d81599e

…Ts (python#148704) Export a few more functions required for external JITs

pythongh-133403: Add type annotations to generate_levenshtein_example…

28b8d5f

…s.py (python#143317) Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

pythongh-148406: Fix annotations of _colorize.FancyCompleter (python#…

4b33308

…148408) Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Prevent GitHub's web conflict editor from converting LF to CRLF (pyth…

9e23652

…on#148739)

sethmlarson and others added 30 commits April 22, 2026 19:22

pythongh-90309: Base64-encode cookie values embedded in JS

76b3923

Update Objects/sentinelobject.c

a851235

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>

pythongh-148883: Docs: clarify grammar in Counter dictionary methods …

79321fd

…note (pythongh-148882)

pythongh-146553: Fix infinite loop in typing.get_type_hints() on circ…

be833e6

…ular __wrapped__ (python#148595)

pythongh-145056: Add support for frozendict in dataclass asdict and a…

8e43f3d

…stuple (python#145125)

pythongh-145194: Fix typing in re tokenizer example (python#145198)

bd7352d

Speed up counting in statistics.fmean() (pythongh-148875)

fbc7676

fix

2beb1c2

pythongh-148892: Drop mention of deprecated cibuildwheel option (pyth…

3b93979

…on#148893)

pythongh-148907: fix performance regression in `PyType_GetModuleByDef…

29917d5

…` on free-threading (python#148908)

pythonGH-126910: Build/link the JIT shim in the Python interpreter (p…

9633c52

…ython#148872)

pythongh-148680: Replace internal names with type_reprs of objects in…

158dbbb

… string representations of ForwardRef (python#148682) Co-authored-by: Shamil <ashm.tech@proton.me>

pythongh-148735: Fix a UAF in Element.findtext() (python#148738)

0469e6d

pythongh-148663: Document that calendar.IllegalMonthError inherits …

435be06

…from both `ValueError` and `IndexError` (python#148664) Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> Co-authored-by: Stan Ulbrych <stan@python.org>

pythongh-132631: Fix "I/O operation on closed file" when parsing JSON…

42d645a

… Lines file (python#132632) Co-authored-by: Brian Schubert <brianm.schubert@gmail.com>

Merge branch 'main' into pep661

e2d92a1

Update Doc/c-api/sentinel.rst

53a84b6

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

pythongh-108951: add TaskGroup.cancel() (python#127214)

95559d2

Fixes python#108951 Co-authored-by: sobolevn <mail@sobolevn.me> Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com> Co-authored-by: Guido van Rossum <guido@python.org>

Merge remote-tracking branch 'upstream/main' into pep661

396356e

feedback

bfa98a1

add assert

465061a

another one

70c04a2

more tweaks

7c276c5

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Initial implementation of PEP 661 v2 (sentinels)#4

Initial implementation of PEP 661 v2 (sentinels)#4
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