[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:


New changeset ec4a580f7cada002441ae5611b909d56e3b5b613 by Victor Stinner in 
branch 'main':
bpo-46355: Update pythoncapi_compat project URL (GH-31670)
https://github.com/python/cpython/commit/ec4a580f7cada002441ae5611b909d56e3b5b613


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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

Change by STINNER Victor :


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pull_requests: +29789
pull_request: https://github.com/python/cpython/pull/31670

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

I created bpo-46836: "[C API] Move PyFrameObject to the internal C API".

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:


New changeset ba5725171d9c411fc4764349205eff5cfc028797 by Erlend Egeberg 
Aasland in branch 'main':
bpo-46355: Amend What's New in Python 3.11 C API wording (GH-31288)
https://github.com/python/cpython/commit/ba5725171d9c411fc4764349205eff5cfc028797


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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[Erlend E. Aasland]

Change by Erlend E. Aasland :


--
nosy: +erlendaasland
nosy_count: 4.0 -> 5.0
pull_requests: +29448
pull_request: https://github.com/python/cpython/pull/31288

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[miss-islington]

miss-islington  added the comment:


New changeset a4cb31927a1f0ee31025ea1ca82fcbfad44755dc by Petr Viktorin in 
branch 'main':
bpo-46355: What's New: Note that PyFrameObject are private (GH-31032)
https://github.com/python/cpython/commit/a4cb31927a1f0ee31025ea1ca82fcbfad44755dc


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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[Petr Viktorin]

Petr Viktorin  added the comment:

> I would hope that competent C programmers would know not to read or write to 
> undocumented fields. But if they come from a Python background, that might 
> not be obvious.

Tread carefully when changing decades-old API, documented or not. The docs 
weren't always as useful and complete as they are now.

> If the advice for something is "use Python", we should probably add an API 
> function.

Not really. If PyObject_GetAttrString doesn't add too much overhead, IMO it's 
fine to use it.

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[Petr Viktorin]

Change by Petr Viktorin :


--
nosy: +petr.viktorin
nosy_count: 2.0 -> 3.0
pull_requests: +29215
pull_request: https://github.com/python/cpython/pull/31032

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

I merged my PR so the doc can be reviewed online at 
https://docs.python.org/dev/whatsnew/3.11.html once it will be rendered ;-)

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stage: patch review -> resolved
status: open -> closed

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 0885999a8e5ffad3fae0302675ad0030e33a15af by Victor Stinner in 
branch 'main':
 bpo-46355: Document PyFrameObject and PyThreadState changes (GH-30558)
https://github.com/python/cpython/commit/0885999a8e5ffad3fae0302675ad0030e33a15af


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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[Mark Shannon]

Mark Shannon  added the comment:

Are there any C programming guides we can link to, that explain API use?
I would hope that competent C programmers would know not to read or write to 
undocumented fields. But if they come from a Python background, that might not 
be obvious.

If the advice for something is "use Python", we should probably add an API 
function.

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nosy: +Mark.Shannon

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

> f_lineno: changed, use PyFrame_GetLineNumber()

Oh I was wrong, PyFrame_GetLineNumber() code is the same in Python 3.10. It was 
already a bad idea to read directly the f_lineno member in Python 3.10: 
PyFrame_GetLineNumber() should always be called.

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

Change by STINNER Victor :


--
keywords: +patch
pull_requests: +28759
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/30558

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[issue46355] [C API] Document PyFrameObject and PyThreadState changes and explain how to port code to Python 3.11

[STINNER Victor]

New submission from STINNER Victor :

Python 3.11 made many changes in PyFrameObject and PyThreadState structures. 
Code which accessed directly structure members doesn't build anymore. For 
example, "frame->f_code" is now fails because PyFrameObject.f_code member is 
done. I propose to document these changes and explain how to port code.

I will write a documentation PR.

== PyFrameObject changes ==

PyFrameObject now only creates a Python frame object on demand.

* f_code: removed, use PyFrame_GetCode() instead, warning: it returns a strong 
reference (Py_DECREF is needed)
* f_lineno: changed, use PyFrame_GetLineNumber()
* f_back: changed, use PyFrame_GetBack()
* f_builtins: removed, get the "f_builtins" attribute in Python
* f_globals: removed, get the "f_globals" attribute in Python
* f_locals: removed, get the "f_locals" attribute in Python
* f_valuesstack: removed
* f_stackdepth: removed
* f_gen: removed
* f_lasti: removed, get the "f_lasti" attribute in Python?
* f_iblock: removed
* f_state: removed
* f_blockstack: removed
* f_localsplus: removed

Accessing f_lineno and f_back doesn't fail with a compiler error, but these 
members are filled lazily. If PyFrame_GetLineNumber() is not called, it can 
return 0 even if the frame is running and has a line number. If 
PyFrame_GetBack() is not called, f_back is NULL even if the frame has a next 
outer frame.

== PyThreadState changes ==

* frame: removed, use PyThreadState_GetFrame(), warning: it returns a strong 
reference (Py_DECREF is needed)
* recursion_depth: removed, use (tstate->recursion_limit - 
tstate->recursion_remaining) instead
* stackcheck_counter: removed
* tracing: changed, use PyThreadState_EnterTracing() and 
PyThreadState_LeaveTracing(), added by bpo-43760

== Notes ==

We should also explain how to get new C API functions, like PyFrame_GetCode(), 
on older Python, and maybe suggest to use pythoncapi_compat to get them:

   https://github.com/pythoncapi/pythoncapi_compat


See also:

* bpo-39947: "[C API] Make the PyThreadState structure opaque (move it to the 
internal C API)"
* bpo-40421: "[C API] Add getter functions for PyFrameObject and maybe move 
PyFrameObject to the internal C API"
* bpo-43760: "The DISPATCH() macro is not as efficient as it could be (move 
PyThreadState.use_tracing)" -- add PyThreadState_EnterTracing()

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components: C API
messages: 410398
nosy: vstinner
priority: normal
severity: normal
status: open
title: [C API] Document PyFrameObject and PyThreadState changes and explain how 
to port code to Python 3.11
versions: Python 3.11

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