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Jan 13, 2022
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bpo-46355: Document PyFrameObject and PyThreadState changes #30558

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bpo-46355: Document PyFrameObject and PyThreadState changes
vstinner Jan 12, 2022
2d020f2
f_lineno didn't change, I was wrong
vstinner Jan 12, 2022
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104 changes: 104 additions & 0 deletions Doc/whatsnew/3.11.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -752,6 +752,110 @@ 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:

* ``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_builtins``: removed,
use ``PyObject_GetAttrString(frame, "f_builtins")``.
* ``f_globals``: removed,
use ``PyObject_GetAttrString(frame, "f_globals")``.
* ``f_locals``: removed,
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 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
computed lazily. The :c:func:`PyFrame_GetBack` function must be called
instead.
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I created https://bugs.python.org/issue46356 to propose to enforce the usage of PyFrame_GetBack() on Python 3.11 to make the C API less error prone.


Code defining ``PyFrame_GetCode()`` on Python 3.8 and older::

#if PY_VERSION_HEX < 0x030900B1
static inline PyCodeObject* PyFrame_GetCode(PyFrameObject *frame)
{
Py_INCREF(frame->f_code);
return frame->f_code;
}
#endif

Code defining ``PyFrame_GetBack()`` on Python 3.8 and older::

#if PY_VERSION_HEX < 0x030900B1
static inline PyFrameObject* PyFrame_GetBack(PyFrameObject *frame)
{
Py_XINCREF(frame->f_back);
return frame->f_back;
}
#endif

Or use `the pythoncapi_compat project
<https://github.com/pythoncapi/pythoncapi_compat>`__ to get these functions
on old Python functions.

* Changes of the :c:type:`PyThreadState` structure members:

* ``frame``: removed, use :c:func:`PyThreadState_GetFrame` (function added
to Python 3.9 by :issue:`40429`).
Warning: the function returns a :term:`strong reference`, need to call
:c:func:`Py_XDECREF`.
* ``tracing``: changed, use :c:func:`PyThreadState_EnterTracing`
and :c:func:`PyThreadState_LeaveTracing`
(functions added to Python 3.11 by :issue:`43760`).
* ``recursion_depth``: removed,
use ``(tstate->recursion_limit - tstate->recursion_remaining)`` instead.
* ``stackcheck_counter``: removed.

Code defining ``PyThreadState_GetFrame()`` on Python 3.8 and older::

#if PY_VERSION_HEX < 0x030900B1
static inline PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
{
Py_XINCREF(tstate->frame);
return tstate->frame;
}
#endif

Code defining ``PyThreadState_EnterTracing()`` and
``PyThreadState_LeaveTracing()`` on Python 3.10 and older::

#if PY_VERSION_HEX < 0x030B00A2
static inline void PyThreadState_EnterTracing(PyThreadState *tstate)
{
tstate->tracing++;
#if PY_VERSION_HEX >= 0x030A00A1
tstate->cframe->use_tracing = 0;
#else
tstate->use_tracing = 0;
#endif
}

static inline void PyThreadState_LeaveTracing(PyThreadState *tstate)
{
int use_tracing = (tstate->c_tracefunc != NULL || tstate->c_profilefunc != NULL);
tstate->tracing--;
#if PY_VERSION_HEX >= 0x030A00A1
tstate->cframe->use_tracing = use_tracing;
#else
tstate->use_tracing = use_tracing;
#endif
}
#endif

Or use `the pythoncapi_compat project
<https://github.com/pythoncapi/pythoncapi_compat>`__ to get these functions
on old Python functions.


Deprecated
----------
Expand Down