bpo-39674: Suggest to test with DeprecationWarning (GH-18552)

Add a section in What's New In Python 3.9 to strongly advice to check
for DeprecationWarning in your Python projects.

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>
This commit is contained in:
Victor Stinner 2020-03-03 22:52:20 +01:00 committed by GitHub
parent 469325c30e
commit 116fd4af73
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 28 additions and 0 deletions

View File

@ -66,6 +66,34 @@ Summary -- Release highlights
.. PEP-sized items next.
You should check for DeprecationWarning in your code
====================================================
When Python 2.7 was still supported, many functions were kept for backward
compatibility with Python 2.7. With the end of Python 2.7 support, these
backward compatibility layers have been removed, or will be removed soon.
Most of them emitted a :exc:`DeprecationWarning` warning for several years. For
example, using ``collections.Mapping`` instead of ``collections.abc.Mapping``
emits a :exc:`DeprecationWarning` since Python 3.3, released in 2012.
Test your application with the :option:`-W` ``default`` command-line option to see
:exc:`DeprecationWarning` and :exc:`PendingDeprecationWarning`, or even with
:option:`-W` ``error`` to treat them as errors. :ref:`Warnings Filter
<warning-filter>` can be used to ignore warnings from third-party code.
It has been decided to keep a few backward compatibility layers for one last
release, to give more time to Python projects maintainers to organize the
removal of the Python 2 support and add support for Python 3.9.
Aliases to ref:`Abstract Base Classes <collections-abstract-base-classes>` in
the :mod:`collections` module, like ``collections.Mapping`` alias to
:class:`collections.abc.Mapping`, are kept for one last release for backward
compatibility. They will be removed from Python 3.10.
More generally, try to run your tests in the :ref:`Python Development Mode
<devmode>` which helps to prepare your code to make it compatible with the
next Python version.
New Features
============