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bpo-39573: Py_TYPE becomes a static inline function #26493

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merged 1 commit into from Jun 3, 2021
Merged

bpo-39573: Py_TYPE becomes a static inline function #26493

merged 1 commit into from Jun 3, 2021
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@vstinner vstinner commented Jun 2, 2021 •
edited by bedevere-bot

Convert the Py_TYPE() and Py_SIZE() macros to static inline
functions. The Py_SET_TYPE() and Py_SET_SIZE() functions must now be
used to set an object type and size.

https://bugs.python.org/issue39573
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bpo-39573: Py_TYPE becomes a static inline function
a379611 
Convert the Py_TYPE() and Py_SIZE() macros to static inline
functions. The Py_SET_TYPE() and Py_SET_SIZE() functions must now be
used to set an object type and size.
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@vstinner vstinner commented Jun 2, 2021

One year ago, I already pushed the same change to Python 3.10, but it broke many projects and so had to be reverted, see: https://bugs.python.org/issue39573#msg370074

Multiple things changed since my latest attempt:

  • Major projects like Cython and numpy have been prepared for this incompatible change

  • I created the https://github.com/pythoncapi/pythoncapi_compat project which is made of two parts:

    • pythoncapi_compat.h header file provides Py_SET_TYPE() and Py_SET_TYPE() to old Python versions: it supports Python 2.7-3.11.
    • upgrade_pythoncapi.py script automates the migration of existing C extensions to the new API (Py_SET_TYPE, Py_SET_TYPE) without losing support with Python 2.7-3.8.

  • pythoncapi_compat.h header and upgrade_pythoncapi.py script have been used successfully on multiple projects (bitarray, immutables, Mercurial, python-zstandard). These projects now include a copy of pythoncapi_compat.h to support old Python versions.

Note: C extensions implemented with Cython only have to regenerate the C files using Cython, if it's not already done (Cython was fixed one year ago).
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@vstinner vstinner commented Jun 2, 2021

More info about the pythoncapi_compat project: https://vstinner.github.io/pythoncapi_compat.html
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@vstinner vstinner commented Jun 3, 2021

The previous attempt (reverted change) was: #20290
@vstinner vstinner merged commit f3fa63e into python:main Jun 3, 2021
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@vstinner vstinner deleted the vstinner:py_type branch Jun 3, 2021
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@vstinner vstinner commented Jun 3, 2021

I prefer to merge such incompatible change early in 3.11 dev cycle to give more test to users to test it. If things go wild again, we can consider to revert it a second time.
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