The Python Software Foundation has released the second release candidate (RC) of Python 3.9 and is warning users to watch for deprecation warnings as it drops backward compatibility for unsupported Python 2.7.
Python maintainers stopped supporting Python 2.7 this April[1], some five years after support was originally meant to end – and 12 years after Python creator Guido van Rossum[2] announced Python 3.
The main highlight from Python 3.9 RC2[3] is that it removes most backward-compatibility layers for Python 2.7. Python 3.8 had those layers; however, it was released in October 2019 when Python 2.7 remained supported.
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The final version of Python 3.9 is scheduled for release in early October, so Python maintainers believe it makes sense to remove the 2.7 compatibility layers.
"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," the Python Software Foundation notes[5].
As explained, even while backward compatibility with Python 2.7 has been available until now, compatibility layers have been emitting a "DeprecationWarning" warning for several years.
Despite the majority of compatibility layers vanishing in Python 3.9, it's been decided to make a few exceptions for some 2.7 compatibility laters to support Python projects maintainers, so that they have time to remove Python 2 support and add support for Python 3.9.
The move to retain some compatibility layers follows concerns raised by RedHat-backed Python maintainer Victor Stinner, who maintains upstream Python and downstream Python for Red Hat Enterprise Linux (RHEL) and Fedora.
Stinner and and fellow RedHat engineer Miro Hrončok in