What’s New in Python 3.9? Key Features, Syntax Tweaks, and Performance Gains

Python 3.9 Official Release

Python 3.9 and later versions no longer support Windows 7; users still on Windows 7 are encouraged to upgrade to Windows 10. The default download is now 64‑bit instead of 32‑bit.

New Syntax Features

PEP 584 : Adds the dictionary union (|) operator.

PEP 585 : Enables generic type hints for built‑in collections, allowing list and dict to be used directly in annotations.

PEP 614 : Removes restrictions on decorator syntax; any legal expression can now be used as a decorator.

PEP 616 : Introduces str.removeprefix() and str.removesuffix() methods.

New Built‑in Features

PEP 614 (continued): Allows any valid expression as a decorator.

Standard Library Additions

PEP 593 : Flexible function and variable annotations. os.pidfd_open(): Enables process management without race conditions or signals.

Interpreter Improvements

PEP 573 : Fast access to module state from C‑extension methods.

PEP 617 : CPython now uses a new PEG‑based parser, offering greater flexibility while matching the performance of the previous LL(1) parser.

PEP 590 : Built‑in objects such as range, tuple, set, frozenset, list, and dict gain speed via the vectorcall protocol.

Performance Benchmarks

A simple timeit test shows roughly a one‑third speed improvement for dict() and range(10) operations compared with Python 3.8.

Garbage Collection and Module Initialization

Garbage collection no longer blocks on resurrected objects.

Many standard‑library modules now use multiphase initialization as defined by PEP 489.

Several modules adopt the stable ABI defined by PEP 384.

New Standard Library Modules

zoneinfo

(PEP 615): Provides IANA time‑zone database support. graphlib: Supplies a topological sort implementation for graphs.

Release Process Changes

PEP 602 : CPython adopts an annual release cycle, with major versions scheduled for October each year.

Interested users can download the new version to try it out.