The stable release of Python 3.15.0, with 5,643 commits from 1,012 contributors: sentinel and frozendict built-ins, UTF-8 by default, explicit lazy imports, unpacking in comprehensions, a significantly faster experimental JIT, the Tachyon sampling profiler, new typing features, a stable ABI for free-threaded builds, and frame pointers enabled by default.

This is the stable release of Python 3.15.0

Python 3.15.0 is the newest major release of the Python programming language, and it contains many new features and optimisations compared to Python 3.14, in 5,643 commits from 1,012 contributors.

Major new features of the 3.15 series, compared to 3.14

Some of the major new features and changes in Python 3.15 are:

Interpreter improvements

PEP 661: Add sentinel built-in type
PEP 686: Python now uses UTF-8 as the default encoding
PEP 798: Unpacking in comprehensions
PEP 810: Explicit lazy imports for faster startup times
PEP 814: Add frozendict built-in type
PEP 829: Package startup configuration files
The experimental JIT compiler has been significantly upgraded, with 7-8% geometric mean performance improvement on x86-64 Linux over the standard interpreter, and 11-12% speedup on AArch64 macOS over the tail-calling interpreter
Improved error messages

Significant improvements in the standard library

PEP 799: A dedicated profiling package for organizing Python profiling tools
PEP 799: Tachyon: High frequency statistical sampling profiler
More color

New typing features

PEP 728: TypedDict with typed extra items
PEP 747: Annotating type forms with TypeForm
PEP 800: Disjoint bases in the type system

C API improvements

PEP 782: A new PyBytesWriter C API to create a Python bytes object
PEP 788: Protection against finalization in the C API
PEP 803, 820, 793: Stable ABI for free-threaded builds and related C API

Build changes

PEP 831: Frame pointers are enabled by default for improved system-level observability

Release changes

The official Windows 64-bit binaries now use the tail-calling interpreter
The official macOS binaries now install free-threading support by default

For more details on the changes to Python 3.15, see What’s new in Python 3.15.

Attention macOS 27.0 `IDLE` or `tkinter` users

When running IDLE or other GUI applications that use the tkinter module, these applications may hang when using an application's menu command that opens a dialog (for example, IDLE's About IDLE, Settings, and Open Module commands) resulting in a spinning beach ball with Force Quit needed.

This problem is due to an operating system behavior change in macOS 27.0 that is believed to affect all current versions of the Tk graphics toolkit and thus the tkinter module in all current Python versions.

If you depend on Tk-based applications (like IDLE) on macOS, you may want to consider deferring installing macOS 27.0 until a Tk or macOS workaround is available or testing that your application workflow is not affected. Follow issue #158053 for updates.

More resources

Online documentation
PEP 790, 3.15 release schedule
Report bugs at https://github.com/python/cpython/issues
Help fund Python directly (or via GitHub Sponsors) and support the Python community

And now for something completely different

To celebrate the new 3.15, Barry Warsaw has a present for us!

I had this idea to whip up a little TUI adventure game that takes you through a What’s New in Python 3.15. I present to you “whatsnewt”:

From the README:

A TUI text adventure through what’s new in Python 3.15.

You wake up in the Startup Foyer, somewhere inside the interpreter, and work your way to the Release Gate. Along the way there are eighteen puzzles, and every one of them is a real 3.15 feature you have to actually use. You’re not just answering boring questions, you’re actually writing and running code, in a Python 3.15 interpreter.

Some puzzles require a type checker, and in those cases, answers are verified by pyrefly, which is a dependency for exactly that reason, and the verdict quotes what it says back.

The easiest way to play it is to run:

uvx --python 3.15 whatsnewt

And yes, there are easter eggs

Enjoy the new release

Thanks to all of the many volunteers who help make Python development and these releases possible! Please consider supporting our efforts by volunteering yourself or through organisation contributions to the Python Software Foundation.

Huge thanks to Georgi Ker and Marie Nordin for the Python 3.15 logo!

And also huge thanks to the Sovereign Tech Agency for supporting Hugo van Kemenade's work as release manager for Python 3.14 and 3.15 through the Sovereign Tech Fellowship.

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