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bpo-46355: What's New: Note that PyFrameObject are private #31032

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Feb 1, 2022
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bpo-46355: What's New: Note that PyFrameObject are private #31032

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29 changes: 20 additions & 9 deletions Doc/whatsnew/3.11.rst
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Expand Up @@ -759,12 +759,19 @@ Porting to Python 3.11
which are not available in the limited C API.
(Contributed by Victor Stinner in :issue:`46007`.)

* Changes of the :c:type:`PyFrameObject` structure members:
* Changes of the private :c:type:`PyFrameObject` structure members.

While the documentation notes that the fields of ``PyFrameObject`` are
subject to change at any time, they have been stable for a long time
and were used in several popular extensions.
In Python 3.11, the frame struct was reorganized to allow performance
optimizations. Rather than reading the fields directly, extensions should
use functions:

* ``f_code``: removed, use :c:func:`PyFrame_GetCode` instead.
Warning: the function returns a :term:`strong reference`, need to call
:c:func:`Py_DECREF`.
* ``f_back``: changed, use :c:func:`PyFrame_GetBack`.
* ``f_back``: changed (see below), use :c:func:`PyFrame_GetBack`.
* ``f_builtins``: removed,
use ``PyObject_GetAttrString(frame, "f_builtins")``.
* ``f_globals``: removed,
Expand All @@ -773,13 +780,17 @@ Porting to Python 3.11
use ``PyObject_GetAttrString(frame, "f_locals")``.
* ``f_lasti``: removed,
use ``PyObject_GetAttrString(frame, "f_lasti")``.
* ``f_valuesstack``: removed.
* ``f_stackdepth``: removed.
* ``f_gen``: removed.
* ``f_iblock``: removed.
* ``f_state``: removed.
* ``f_blockstack``: removed.
* ``f_localsplus``: removed.

The following fields were removed entirely, as they were details
of the old implementation:

* ``f_valuesstack``
* ``f_stackdepth``
* ``f_gen``
* ``f_iblock``
* ``f_state``
* ``f_blockstack``
* ``f_localsplus``

The Python frame object is now created lazily. A side effect is that the
``f_back`` member must not be accessed directly, since its value is now also
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