Release Date: Feb. 16, 2021

This is the release candidate of the second maintenance release of Python 3.9

Note: The release you're looking at is Python 3.9.2rc1, a release candidate of a bugfix release for the legacy 3.9 series. Python 3.11 is now the latest feature release series of Python 3. Get the latest release of 3.11.x here.

We've made 161 commits since 3.9.1, among which you can find two security fixes:

• bpo-42967: Fix web cache poisoning vulnerability by defaulting the query args separator to &, and allowing the user to choose a custom separator.

• bpo-42938: Avoid static buffers when computing the repr of ctypes.c_double and ctypes.c_longdouble values.

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 573, Module State Access from C Extension Methods
• 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 614, Relaxing Grammar Restrictions On Decorators
• 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.

You can find a more comprehensive list in this release's "What's New" document.

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

Professor (Eric Idle): It's an entirely new strain of sheep, a killer sheep that can not only hold a rifle but is also a first-class shot.
Assistant (Carol Cleveland): But where are they coming from, professor?
Professor: That I don't know. I just don't know. I really just don't know. I'm afraid even I really just don't know. I have to tell you I'm afraid even I really just don't know. I'm afraid I have to tell you...
(she hands him a glass of water which she had been busy getting as soon as he started into this speech) ... thank you ... (resuming normal breezy voice)
Professor: ... I don't know. Our only clue is this portion of wolf's clothing which the killer sheep...
Viking (Terry Gilliam): ... was wearing...
Professor: ... in yesterday's raid on Selfridges.

Full Changelog