Python 3.9.0b4

Release date: July 3, 2020

This is a beta preview of Python 3.9

Python 3.9 is still in development. This release, 3.9.0b4, is the fourth of five planned beta release previews. Beta release previews are intended to give the wider community the opportunity to test new features and bug fixes and to prepare their projects to support the new feature release.

Call to action

We strongly encourage maintainers of third-party Python projects to test with 3.9 during the beta phase and report issues found to the Python bug tracker as soon as possible. While the release is planned to be feature complete entering the beta phase, it is possible that features may be modified or, in rare cases, deleted up until the start of the release candidate phase (2020-08-10). Our goal is have no ABI changes after beta 5 and as few code changes as possible after 3.9.0rc1, the first release candidate. To achieve that, it will be extremely important to get as much exposure for 3.9 as possible during the beta phase.

Please keep in mind that this is a preview release and its use is not recommended for production environments.

Major new features of the 3.9 series, compared to 3.8

Some of the new major new features and changes in Python 3.9 are:

• PEP 584, Union Operators in dict
• PEP 585, Type Hinting Generics In Standard Collections
• PEP 593, Flexible function and variable annotations
• PEP 602, Python adopts a stable annual release cadence
• PEP 615, Support for the IANA Time Zone Database in the Standard Library
• PEP 616, String methods to remove prefixes and suffixes
• PEP 617, New PEG parser for CPython
• BPO 38379, garbage collection does not block on resurrected objects;
• BPO 38692, os.pidfd_open added that allows process management without races and signals;
• BPO 39926, Unicode support updated to version 13.0.0;
• BPO 1635741, when Python is initialized multiple times in the same process, it does not leak memory anymore;
• A number of Python builtins (range, tuple, set, frozenset, list, dict) are now sped up using PEP 590 vectorcall;
• A number of Python modules (_abc, audioop, _bz2, _codecs, _contextvars, _crypt, _functools, _json, _locale, operator, resource, time, _weakref) now use multiphase initialization as defined by PEP 489;

• A number of standard library modules (audioop, ast, grp, _hashlib, pwd, _posixsubprocess, random, select, struct, termios, zlib) are now using the stable ABI defined by PEP 384.

• (Hey, fellow core developer, if a feature you find important is missing from this list, let Łukasz know.)

The next pre-release, the fifth beta release of Python 3.9, will be 3.9.0b5. It is currently scheduled for 2020-07-20.

More resources

• Online Documentation
• PEP 596, 3.9 Release Schedule
• Report bugs at https://bugs.python.org.
• Help fund Python and its community.

And now for something completely different

(Cut to a newsreader in a 'News at Nine' set with a bare lightbulb hanging in shot. He wears only an old blanket around his shoulders. He is shivering.)

Newsreader (Eric Idle): The BBC wishes to deny rumours that it is going into liquidation. Mrs Kelly, who owns the flat where they live, has said that they can stay on till the end of the month...
(he is handed a piece of paper)
Newsreader: ...and we've just heard that Hugh Weldon's watch has been accepted by the London Electricity Board and transmissions for this evening can be continued as planned.
(he coughs and pulls the blanket tighter round his shoulders)
Newsreader: That's all from me so... goodnight.

Full Changelog