Python 3.8.0b4

Release Date: Aug. 29, 2019

This is a beta preview of Python 3.8

Python 3.8 is still in development. This release, 3.8.0b4 is the last of four 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 3.8 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 (2019-09-30). Our goal is have no ABI changes after beta 3 and no code changes after 3.8.0rc1, the release candidate. To achieve that, it will be extremely important to get as much exposure for 3.8 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 3.8 series, compared to 3.7

Some of the new major new features and changes in Python 3.8 are:

PEP 572, Assignment expressions

PEP 570, Positional-only arguments

PEP 587, Python Initialization Configuration (improved embedding)

PEP 590, Vectorcall: a fast calling protocol for CPython

PEP 578, Runtime audit hooks

PEP 574, Pickle protocol 5 with out-of-band data

Typing-related: PEP 591 (Final qualifier), PEP 586 (Literal types), and PEP 589 (TypedDict)

Parallel filesystem cache for compiled bytecode

Debug builds share ABI as release builds

f-strings support a handy = specifier for debugging

specifier for debugging continue is now legal in finally: blocks

is now legal in blocks on Windows, the default asyncio event loop is now ProactorEventLoop

event loop is now on macOS, the spawn start method is now used by default in multiprocessing

multiprocessing can now use shared memory segments to avoid pickling costs between processes

can now use shared memory segments to avoid pickling costs between processes typed_ast is merged back to CPython

is merged back to CPython LOAD_GLOBAL is now 40% faster

is now 40% faster pickle now uses Protocol 4 by default, improving performance

now uses Protocol 4 by default, improving performance (Hey, fellow core developer, if a feature you find important is missing from this list, let Łukasz know.)

There are many other interesting changes, please consult the "What's New" page in the documentation for a full list.

The next pre-release of Python 3.8 and the first release candidate will be 3.8.0rc1, currently scheduled for 2019-09-30.

More resources

And now for something completely different

Mr Neutron! The most dangerous and terrifying man in the world! The man with the strength of an army! The wisdom of all the scholars in history! The man who had the power to destroy the world.

✨ 🌍 🌎 🌏 🌍 🌎 🌏 ✨

Mr Neutron. No one knows what strange and distant planet he came from, or where he was going to!... Wherever he went, terror and destruction were sure to follow.

Full Changelog