Python 3.9 Release History

Python 3.9 (released October 5, 2020) introduced major internal improvements and laid the groundwork for future language features.

Major Highlight: PEG Parser

One of the most important changes is the switch to a PEG parser (PEP 617).

• More flexible than the old LL(1) parser
• Enables future syntax improvements
• Foundation for features like pattern matching (Python 3.10)

Performance remains similar, but extensibility is significantly improved :contentReference[oaicite:6]{index=6}

Dict Union Operators (| and |=)

PEP 584 introduced intuitive dictionary merging:

x = {"a": 1}
y = {"a": 2, "b": 3}

z = x | y
# {'a': 2, 'b': 3}

• Cleaner than dict.update() or unpacking
• Supports both merge and in-place update ([Python documentation][1])

New String Methods

PEP 616:

• str.removeprefix()
• str.removesuffix()

Safer and more predictable than using .strip() ([Python documentation][1])

Built-in Generic Types

PEP 585:

• Use built-in collections as generics:

def func(data: list[str]): ...

• No need to import from typing ([Python documentation][1])

Standard Library

• New zoneinfo module (IANA time zones)
• New graphlib module for topological sorting
• Improvements across multiple modules ([Python documentation][1])

Performance Improvements

• Faster built-in types (list, dict, etc.)
• Adoption of vectorcall (PEP 590)
• Improved garbage collection and module initialization ([Python documentation][1])

Deprecations

• Old LL(1) parser deprecated
• parser module deprecated
• Ongoing cleanup of legacy APIs

Subversions log

• 3.9.23 (Jul 2025) — final security updates
• 3.9.19 (Mar 2024) — cumulative fixes
• 3.9.10 (Jan 2022) — memory and module fixes
• 3.9.1 (Dec 2020) — Apple Silicon support
• 3.9.0 (Oct 2020) — initial release

Official 3.9 documentation