[issue39674] Keep deprecated features in Python 3.9 to ease migration from Python 2.7, but remove in Python 3.10

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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pull_requests: +18133
pull_request: https://github.com/python/cpython/pull/18776

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39674>
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