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****************************
What's New In Python 3.9
****************************
:Release: |release|
:Date: |today|
.. Rules for maintenance:
* Anyone can add text to this document. Do not spend very much time
on the wording of your changes, because your text will probably
get rewritten to some degree.
* The maintainer will go through Misc/NEWS periodically and add
changes; it's therefore more important to add your changes to
Misc/NEWS than to this file.
* This is not a complete list of every single change; completeness
is the purpose of Misc/NEWS. Some changes I consider too small
or esoteric to include. If such a change is added to the text,
I'll just remove it. (This is another reason you shouldn't spend
too much time on writing your addition.)
* If you want to draw your new text to the attention of the
maintainer, add 'XXX' to the beginning of the paragraph or
section.
* It's OK to just add a fragmentary note about a change. For
example: "XXX Describe the transmogrify() function added to the
socket module." The maintainer will research the change and
write the necessary text.
* You can comment out your additions if you like, but it's not
necessary (especially when a final release is some months away).
* Credit the author of a patch or bugfix. Just the name is
sufficient; the e-mail address isn't necessary.
* It's helpful to add the bug/patch number as a comment:
XXX Describe the transmogrify() function added to the socket
module.
(Contributed by P.Y. Developer in :issue:`12345`.)
This saves the maintainer the effort of going through the Mercurial log
when researching a change.
This article explains the new features in Python 3.9, compared to 3.8.
For full details, see the :source:`Misc/NEWS` file.
.. note::
Prerelease users should be aware that this document is currently in draft
form. It will be updated substantially as Python 3.9 moves towards release,
so it's worth checking back even after reading earlier versions.
Summary -- Release highlights
=============================
.. This section singles out the most important changes in Python 3.9.
Brevity is key.
.. PEP-sized items next.
New Features
============
Other Language Changes
======================
New Modules
===========
* None yet.
Improved Modules
================
threading
---------
In a subinterpreter, spawning a daemon thread now raises an exception. Daemon
threads were never supported in subinterpreters. Previously, the subinterpreter
finalization crashed with a Pyton fatal error if a daemon thread was still
running.
Optimizations
=============
Build and C API Changes
=======================
* Add a new public :c:func:`PyObject_CallNoArgs` function to the C API:
call a callable Python object without any arguments.
Deprecated
==========
* Currently :func:`math.factorial` accepts :class:`float` instances with
non-negative integer values (like ``5.0``). It raises a :exc:`ValueError`
for non-integral and negative floats. It is deprecated now. In future
Python versions it will raise a :exc:`TypeError` for all floats.
(Contributed by Serhiy Storchaka in :issue:`37315`.)
Removed
=======
``_dummy_thread`` and ``dummy_threading`` modules have been removed. These
modules were deprecated since Python 3.7 which requires threading support.
(Contributed by Victor Stinner in :issue:`37312`.)
Porting to Python 3.9
=====================
This section lists previously described changes and other bugfixes
that may require changes to your code.
|
