Victor Stinner

My recent work on PyBytesWriter and PyUnicodeWriter C API, bugfixes, optimizations, and documentation changes: vstinner.github.io/optimize-pyb... PyBytesWriter is now 1.28x faster than Python 3.15 and PyUnicodeWriter can avoid memory copies. Detect buffer overflow in debug mode.

It’s been a while, but Core Dispatch 11 is out! Happy Python 3.15 final day to all that celebrate! Congrats to @hugovk.dev on getting the release across the finish line! 🎉 Catch up on what’s been happening in CPython: coredispatch.xyz/editions/11

I just optimized PyFloat_PackN() C functions in Python using __builtin_bswapN() to swap bytes. Problem: GCC does crash and clang miscompiles the 16-bit function which uses _Float16 on IBM s390x! GCC bug report: bugzilla.redhat.com/show_bug.cgi... clang bug report: github.com/llvm/llvm-pr...

Interesting discussions on new convenient APIs to start Python threads: run(func, *args), with ThreadManager(), and ThreadSet: discuss.python.org/t/add-a-thre...

New long article on PEP 814: Add frozendict built-in type vstinner.github.io/pep-814-add-... Donghee Na and me wrote PEP 814 to add frozendict implemented in C. Here is the long journey of adding the type to Python 3.15: implementation, stdlib changes, optimizations, complex bugs, C API, etc.

I'm writing an article series on Free Threading internals. The 3rd article vstinner.github.io/free-threadi... introduces PyMutex: one byte lock with fast, inlineable lock and unlock functions for the common uncontended case. The design is based on WebKit's WTF::Lock.

The Python test suite now pass on Alpine Linux (musl C library): discuss.python.org/t/the-python... I increased the stack size to 1 MiB and skipped the few tests known to fail on musl.

I'm writing an article serie on Free Threading internals. The second article vstinner.github.io/free-threadi... analyzes immortal objects, deferred reference count, and stack references which reduce reference count contention by optimizing Py_INCREF()/Py_DECREF().

Article serie on Free Threading internals. First article on the performance problem of tracking objects lifetime: vstinner.github.io/free-threadi... Gilectomy started with atomic operations and switched to buffered ref counting. nogil solved the perf issue using Biased Reference Counting.

Frame pointers? Frame pointers! peps.python.org/pep-0831/

Nearly 5 years, countless PRs, a program grown from 1 to 5. Thank you, Łukasz Langa, for defining the CPython Developer in Residence role. Best of luck on the next step of your journey and we'll see you around the community!

Please welcome Stan Ulbrych as the newest member of the Python core team! discuss.python.org/t/vote-to-pr... hugovk.github.io/python-core-... #Python #CPython #CoreTeam

Core Dispatch #1 New releases are slated to drop on Monday: 3.13.13, 3.14.4, and 3.15.0a8. PEP 803 got accepted, so free-threaded builds will have a stable ABI. Ken Jin also wrote up what's going on with the JIT in 3.15. coredispatch.xyz/editions/1

Just posted the Rust for CPython Progress Update for April 2026 to the Python Insider Blog! This covers what we've been up to and our roadmap to a PEP. If you're interested in contributing please join our Discord! blog.python.org/2026/04/rust...

More in this 3.15 alpha: 🖨️ pprint: new `expand` arg for Black-like output (let's make it default?) 🧛 bytes.replace() count arg can be a keyword 🌊 wave: IEEE floating-point WAVE audio support, new getformat()/setformat() ⏱️ timeit: configurable target time for autorange() #Python #Python315 #release

New in this alpha: 🧵 PEP 803: “abi3t”: Stable ABI for free-threaded builds 🪟 Official Windows 64-bit binaries now use the tail-calling interpreter for up to 40% speedup! docs.python.org/3.15/whatsne... 🦋 REPL: colour tab completion with fancycompleter #Python #Python315 #release

New releases! 🐍 Python 3.15.0a8! 🐍 Python 3.14.4! 🐍 Python 3.13.3! 🖼️ Pillow 12.2.0! blog.python.org/2026/04/pyth... pillow.readthedocs.io/en/latest/re... ⚠️ This is the final 3.15 alpha: only 4 weeks until the feature freeze! 🧊 #Python #Python313 #Python314 #Python315 #Pillow #release

Brocards for vulnerability triage https://blog.yossarian.net/2026/04/11/Brocards-for-vulnerability-triage #security #oss

📣 L’AFPy a besoin de vous pour trouver un lieu pour la PyConFR 2026. L’événement doit normalement se tenir à l’automne prochain mais nous n’avons actuellement trouvé aucun local pour nous accueillir. La PyConFR est un événement gratuit pour ses participant·e·s […] [Original post on mamot.fr]

Happy to share that PEP 803 has been accepted. A meaningful step toward Stable ABI for free threading in Python 3.15, with clear importance for C extension support. discuss.python.org/t/pep-803-st...

Please welcome the newest member to the CPython core team, Itamar Oren! discuss.python.org/t/vote-to-pr... hugovk.github.io/python-core-... #Python #CPython #CoreTeam

Stoked to share that the Steering Council has accepted PEP 814. frozendict is coming to Python 3.15! discuss.python.org/t/pep-814-ad...

Coming soon to Python 3.15: frozendict The Steering Council has just accepted @vstinner.bsky.social and @corona10.bsky.social's PEP 814 "Add frozendict built-in type". discuss.python.org/t/pep-814-ad... peps.python.org/pep-0814/ #Python #PEP814 #frozendict #Python315

I am very happy to share that PEP 814 is accepted. Huge kudos to @vstinner.bsky.social for driving this PEP from the start! discuss.python.org/t/pep-814-ad...

How do you use Python and its related technologies? Let us know in the 2026 Python Developers Survey! 🐍 #python #pythondevsurvey

2025 was another eventful year for PyPI! Critical security enhancements, powerful new org features, a better overall user experience, and transparent security incident response 🎉👏 Thank you, PyPI team & community! Learn more on our blog: blog.pypi.org/posts/2025-1...

I’m happy to announce that the Steering Council has approved my proposal to hold the next Language Summit at @europython.eu 2026 and then alternate with @pycon.us! discuss.python.org/t/language-s... ep2026.europython.eu #Python #LanguageSummit #EuroPython

An introduction to PEP-814: lwn.net/SubscriberLi... My best wishes for having it in 3.15! ❤️🤞🏼

I wrote a new PEP with Donghee Na: "PEP 814: Add frozendict built-in type": discuss.python.org/t/104854 A new public immutable type frozendict is added to the builtins module. The insertion order is preserved and a frozendict can be hashed.

Looking to make a CPython contribution? I'm going to start working on maintaining a "Good First Issue" board for argparse. If you're interested, have a look and let me know on the GitHub issue if you have any questions. Happy to help 🤝🏻! github.com/orgs/python/...

New blog post! Decompression is up to 30% faster in CPython 3.15 This blog goes over a journey to find an optimization in some lower-level code in CPython that yields a speedup of 10-30% when decompressing more than 1MiB of data. emmatyping.dev/decompressio...

Wooo, unanimous acceptance of 810! Python is getting lazy imports! So excited about this! discuss.python.org/t/pep-810-ex...

🎙️ Bored this weekend? Part 2 of the interviews from the CPython core sprint in Cambridge UK is out. Don’t worry, it's shorter than Part 1. Only 2 hours 18 minutes! ✨ Hear from Greg, Thomas, Paul, Pradyun, Carol, Guido, Brett, Erlend, Tal, Lys, Yury, and Diego. creators.spotify.com/pod/profile/...

In the Python C API, I dislike APIs modifying immutable objects like _PyBytes_Resize(). I designed a new PyBytesWriter API to replace this function. As usual in Python, it took multiple iterations and one year to design the API and to reach an agreement. vstinner.github.io/pep-782-pyby...

The future Python 3.15 just got a new os.statx() function thanks to Jeffrey Bosboom! Documentation: docs.python.org/dev/library/... The syscall was added to Linux 4.11 (released in 2017) and glibc 2.28 (2018). For example, it gives access to birthtime, mount ID and subvolume ID.

🚀 Python 3.14 is out and so is 3.15 alpha! I chatted with @hugovk.dev, @pablogsal.com, and @lukasz.langa.pl about which release was the least successful, why release notes always say “and now for something completely different”, how Python actually gets released and many more! youtu.be/BHUWyM2cxwE

Forget* about Python 3.14, the cool kids are on 3.15.0a1! 🚀 🔬 Dedicated profiling package for Python profiling tools 💬 UTF-8 as default encoding 🌊 New C API to create bytes object ⚠️ Better error messages discuss.python.org/t/python-3-1... * Don't forget about 3.14 #Python #Python315 #release

64-bit Raspberry Pi is now supported as a Tier 3 platform 🫡🎉 peps.python.org/pep-0011/

🐍 CPython Core Dev Sprint 2025 wrap: ~50 core devs (yes, Guido too) and invited guests hacking in Cambridge. JIT, free-threading, C-API, endless side discussions. It's safe to say the best ideas start over coffee and a whiteboard with @python.org: community.arm.com/arm-communit...

🐍 Python 3.14 is here! 🎉 ✨ Template strings (t-strings) for safer string interpolation 🚀 Free-threaded Python officially supported (bye GIL!) 🎨 Syntax highlighting in the REPL 📦 Zstandard compression in stdlib 🔍 Remote PDB debugging Full release notes: docs.python.org/3.14/whatsne...

Just released! 🚀 Please install and enjoy Python 3.14! 🥧 discuss.python.org/t/python-3-1... #Python #Python314 #release

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🐍🏃‍➡️ We kicked off the first day of the #Python #CoreSprint at Arm in Cambridge with lots of talks and lots of discussion about talks! Talks about the JIT, WASI, Pyodide PPI, cross-platform wheel builds, demo of new C API, precompiled binaries from python.org, PEP 793 and abi3/abi3t/abi4 discussion

🐍🏃‍➡️🏃‍➡️🏃‍➡️🏃‍➡️ #Python #CoreSprint day 4! Finally, 3.14.0rc3: next RM @savannah.dev joined in to watch the process and ask questions 🥧 Then a quick core․py recording with @pablogsal.com and @lukasz.langa.pl before heading up to Manchester for #PyConUK! 🐝 Thanks again to @diegor.it and Arm for hosting! 🦾

🐍🏃‍➡️🏃‍➡️ #Python #CoreSprint day 3! Lightning talks from Guido van Rossum, Ee Durbin, Steve Dower, Larry Hastings, Adam Turner & Greg Smith Carol Willing, Adam, Thomas Wouters, Petr Viktorin and I discussed a number of docs topics I released the Python Sphinx Docs Theme with more translations SC Q&A

🐍🏃‍➡️🏃‍➡️ #Python #CoreSprint day 2! @ixek.bsky.social gave a mentorship talk @gpshead.bsky.social gave a Claude demo Tania, @jezdez.dev, @willingc.bsky.social and I discussed the User Success WG We ended with punting on the Cam and dinner at Jesus College! @yhg1s.bsky.social ran Feuding Pythonistas.

Design an API can take time. This article describes the design of the C API to import and export Python integers. It takes place between August 2023 and December 2024. In total, the discussions got more than 448 messages! vstinner.github.io/pep-757-c-ap...

Our Python doc is officially out in the wild! 🐍 Thanks to everyone who joined the premiere 🙌 such a good vibe. Here’s the link so you can watch it on repeat youtu.be/GfH4QL4VqJ0

The Python documentary by @cultrepo.bsky.social is going to be debuting live on YouTube on Thursday the 28th at 7pm CET/10am PT! www.youtube.com/@cultrepo I'll share a link the day before to the doc that will have a countdown to the debut. I'm planning to be in the live chat during the debut.

The PSF has adopted pypistats.org, ensuring long-term stability while staying open source and community driven 🎉 Thank you to Christopher Flynn, for operating this awesome community service for 6+ years- and for continuing to maintain the project 💪🐍 pyfound.blogspot.com/2025/08/pypi...