Python 3.15 Release Notes
The Python 3.15 release brings a number of meaningful improvements over version 3.14. Highlights include a high-frequency sampling profiler, UTF-8 set as the default encoding for I/O, a new low-level C API for building bytes objects, and more helpful error messages. The update also introduces various improvements across modules and the C-API.
Summary – Release Highlights
- PEP 799: A dedicated sampling profiler for performance analysis without modifying source code.
- PEP 686: UTF-8 becomes the default encoding when no other encoding is specified.
- PEP 782: Introduction of the
PyBytesWriterC API for efficient bytes object creation. - Improved error messages: when an attribute is missing but a similar attribute exists, Python suggests the correct name.
New Core Features
Important new capabilities include:
-
Sampling profiler: Introduced as
profiling.sampling. This profiler can attach to a running process with very low overhead (sampling rates up to around 1 000 000 Hz), without needing to restart or modify the code. - UTF-8 default encoding: When opening files or performing I/O without specifying an encoding, UTF-8 will now be used by default, improving portability and consistency across platforms.
-
Bytes object building API: The new
PyBytesWriterset of functions (e.g.,PyBytesWriter_Create(),PyBytesWriter_WriteBytes()) allows C-extensions to build bytes objects more efficiently. - Better diagnostics: Error messages have been improved. For example, when you attempt to access a non-existent attribute but a similar one exists in a member object, Python now suggests the correct attribute name.
Other Significant Changes
Python 3.15 also includes many refinements across the standard library and internal APIs:
- Improvements in modules such as
calendar,collections,hashlib,sqlite3, among others. - Removal or deprecation of old or undocumented APIs (for example,
collections.abc.ByteStringhas been removed fromcollections.abc.__all__, scheduled for full removal in future versions). - C API changes and cleanup: underlying extension APIs have been updated (such as new functions replacing older ones in
PyUnicodeorPyImport), aiding future compatibility and performance.
Deprecations & Removals
Developers should take note of several deprecated or removed features:
- Some deprecated modules and functions are removed or flagged for future removal (for example old
NamedTuplesyntax, certainzipimportmethods). - C API cleanup means some older extension functions are no longer available or recommended, and migration to newer APIs is encouraged.
Conclusion
With Python 3.15, the language moves forward in terms of performance tooling, cross-platform consistency, and diagnostics. The defaulting to UTF-8, improved profiling tools, and refined C-APIs help both everyday application developers and extension developers. Although some backward-incompatible changes and removals are included, the release is well-suited for writing safer, more portable and higher-performing Python code.