Python 3.13 Release Notes

Release Date: October 7, 2024

Python 3.13 is a stable release that introduces significant improvements to the interpreter, typing system, and developer experience.

What's New in Python 3.13

Performance Improvements

• Continued CPython optimizations and memory improvements.
• Foundations for future performance features such as JIT compilation.
• Reduced memory usage in some cases (e.g. docstrings and internal structures).

Interpreter and Runtime

• New interactive interpreter (REPL):

  • Multiline editing with history support.
  • Built-in commands like help, exit, quit without parentheses.
  • Syntax highlighting and colored tracebacks by default. :contentReference[oaicite:0]{index=0}

• Experimental free-threaded mode (PEP 703):

  • Optional build without the Global Interpreter Lock (GIL).
  • Enables better multi-core utilization. :contentReference[oaicite:1]{index=1}

• Experimental JIT compiler (PEP 744):

  • Early groundwork for future runtime optimizations. :contentReference[oaicite:2]{index=2}

Language and Typing

• Support for default values in type parameters.

• New typing features:

  • typing.TypeIs for type narrowing.
  • Read-only fields for TypedDict.
  • Type-level deprecation annotations. :contentReference[oaicite:3]{index=3}

• Defined semantics for locals() mutations:

  • Improves debugger and introspection consistency. :contentReference[oaicite:4]{index=4}

Standard Library

• New features and improvements:

  • base64.z85encode() / z85decode() for Z85 encoding.
  • copy.replace() for structured object copying.
  • dbm.sqlite3 becomes the default backend for dbm.
  • New CLI for the random module.
  • New exception: PythonFinalizationError. :contentReference[oaicite:5]{index=5}

• Improvements in modules like argparse, os, ssl, and others.

Platforms and Compatibility

• WASI promoted to Tier 2 support.
• iOS and Android introduced as Tier 3 platforms. :contentReference[oaicite:6]{index=6}

Removals and Deprecations

• Removal of many legacy modules ("dead batteries"), including:
  • cgi, telnetlib, aifc, audioop, and others.
• Ongoing cleanup of deprecated APIs in the standard library and C API. :contentReference[oaicite:7]{index=7}

Migration Notes

Upgrading from Python 3.12 is generally straightforward, but consider:

• Removed deprecated modules and APIs.
• Changes in typing behavior.
• Testing code that depends on internal or undocumented behavior.

Documentation

Official 3.13 documentation