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GeezerVison is showing github.com — gh-141070: Add PyUnstable_Object_Dump() function by vstinner · Pull Request #141072 · python/cpython

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@vstinner

@vstinner vstinner commented Nov 5, 2025 •
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  • Promote _PyObject_Dump() as a public function.
  • Keep _PyObject_Dump() alias to PyUnstable_Object_Dump() for backward compatibility.
  • Replace _PyObject_Dump() with PyUnstable_Object_Dump().
  • Issue: [C API] Promote _PyObject_Dump() to a public function #141070

📚 Documentation preview 📚: https://cpython-previews--141072.org.readthedocs.build/

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@vstinner
pythongh-141070: Add PyObject_Dump() function
2d55425 
* Promote _PyObject_Dump() as a public function.
* Keep _PyObject_Dump() alias to PyObject_Dump() for backward
  compatibility.
* Replace _PyObject_Dump() with PyObject_Dump().
@vstinner
vstinner requested review from AA-Turner, ZeroIntensity and ericsnowcurrently as code owners November 5, 2025 21:10
@bedevere-app bedevere-app Bot added the awaiting core review label Nov 5, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Nov 5, 2025
[C API] Promote _PyObject_Dump() to a public function #141070
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@vstinner

vstinner commented Nov 5, 2025

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cc @ZeroIntensity @picnixz
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@vstinner vstinner added type-feature A feature request or enhancement topic-C-API labels Nov 5, 2025
@vstinner
Fix doc formatting
8abec04
@vstinner vstinner removed the type-feature A feature request or enhancement label Nov 5, 2025
@ZeroIntensity

ZeroIntensity commented Nov 5, 2025

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The tests seem to be failing on Windows.
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@vstinner
Try to fix test on Windows
4338ac0
@vstinner

vstinner commented Nov 5, 2025

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The tests seem to be failing on Windows.

object address : 0000017EAEAFA4D0

Ah yes, printf("%p", ptr) doesn't print 0x prefix on Windows.
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ZeroIntensity
ZeroIntensity approved these changes Nov 5, 2025
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LGTM with a few English nitpicks on the docs.

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Comment thread Doc/c-api/object.rst Resolved

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Comment thread Doc/c-api/object.rst Resolved

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Comment thread Doc/c-api/object.rst Resolved

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Nov 5, 2025
vstinner and others added 3 commits November 6, 2025 00:18
@vstinner @ZeroIntensity
Update Doc/c-api/object.rst
2e982a1 
Co-authored-by: Peter Bierma <[email protected]>
@vstinner @ZeroIntensity
Update Doc/c-api/object.rst
e4c7cdc 
Co-authored-by: Peter Bierma <[email protected]>
@vstinner @ZeroIntensity
Update Doc/c-api/object.rst
c65db8f 
Co-authored-by: Peter Bierma <[email protected]>
kumaraditya303
kumaraditya303 reviewed Nov 6, 2025
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Comment thread Doc/c-api/object.rst Resolved

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kumaraditya303
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@encukou

encukou commented Nov 6, 2025

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I think this is a great candidate for unstable API.
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encukou
encukou reviewed Nov 6, 2025
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Comment thread Doc/c-api/object.rst Resolved

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vstinner and others added 4 commits November 6, 2025 12:07
@vstinner @kumaraditya303
Update Doc/c-api/object.rst
94b9315 
Co-authored-by: Kumar Aditya <[email protected]>
@vstinner @encukou
Enhance the doc
423d25a 
Co-authored-by: Petr Viktorin <[email protected]>
@vstinner
Enhance tests: test NULL and release the GIL
f64a812
@vstinner
The output format may change at any time
bf279d3
@vstinner vstinner mentioned this pull request Nov 6, 2025
Add PyUnstable_Object_Dump() function: promote private _PyObject_Dump() to a public function capi-workgroup/decisions#87
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@vstinner

vstinner commented Nov 6, 2025

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I created a C API Working Group decision issue.
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@vstinner
Fix NULL test on macOS and Windows
70f5433
@ZeroIntensity

ZeroIntensity commented Nov 8, 2025

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Hm, @encukou, why make this an unstable API? I don't think we ever plan to remove the ability to print objects from the C API. If you're concerned about people relying on the exact output, we can just tell them "don't do that" in the docs.
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@encukou

encukou commented Nov 10, 2025 •
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I don't think we ever plan to remove the ability to print objects from the C API.

That we don't, but _PyObject_Dump is about dumping object internals to a fixed stream. AFAICS, it's strictly a debugging tool.

Or is there a use case where you call this from a releasable extension?
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@ZeroIntensity

ZeroIntensity commented Nov 10, 2025

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Or is there a use case where you call this from a releasable extension?

Absolutely, we do it ourselves. It's a convenient debugging tool, but it's also quite handy as a last-ditch effort to display something to the user, like with PyErr_Display.

I think as long as we specify the function as "dump non-specific debugging information about an object", it should be fine to add it as a non-unstable API. If we do add it to PyUnstable, I'd be strongly -1 on any proposal to remove it, which I feel kind of defeats the point of the unstable API in the first place.
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vstinner added 2 commits November 18, 2025 16:34
@vstinner
Rename to PyUnstable_Object_Dump()
56ac7ef
@vstinner
Merge branch 'main' into object_dump
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vstinner
vstinner commented Nov 18, 2025
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Comment thread Doc/whatsnew/3.15.rst

* Add a new :c:func:`PyImport_CreateModuleFromInitfunc` C-API for creating
a module from a *spec* and *initfunc*.
(Contributed by Itamar Oren in :gh:`116146`.)

@vstinner vstinner Nov 18, 2025

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Entries should be sorted.

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@encukou encukou Nov 18, 2025

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I didn't know that. What's the sort key?

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@vstinner vstinner Nov 18, 2025

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"Sorted alphabetically". @hugovk added comments like that in the What's New document:

.. Add C API deprecations above alphabetically, not here at the end.

We should add a similar comment for C API "New features". I think that it was @AA-Turner who started to sort items in What's New In Python 3.14.

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@vstinner
simplify test
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@vstinner

vstinner commented Nov 18, 2025

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I renamed the function to PyUnstable_Object_Dump().
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@vstinner vstinner changed the title gh-141070: Add PyObject_Dump() function gh-141070: Add PyUnstable_Object_Dump() function Nov 18, 2025
@encukou

encukou commented Nov 18, 2025

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Absolutely, we do it ourselves.

That's debugging helper. Unstable API is great for those :)

If we do add it to PyUnstable, I'd be strongly -1 on any proposal to remove it, which I feel kind of defeats the point of the unstable API in the first place.

There's a bunch of unstable API like that -- I think some people would be sad to PyUnstable_Code_GetExtra go, for example.
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@vstinner

vstinner commented Nov 18, 2025

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@ZeroIntensity: I prefer the PyUnstable prefix since the function behavior is not well defined. It can change between Python versions, especially the output, even if it has not changed frequently. Also, this function should only be used for debugging purpose. Well, I proposed PyUnstable_Object_Dump() name to the C API Working Group and it's been accepted (4/5 votes so far).
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vstinner enabled auto-merge (squash) November 18, 2025 16:05
@vstinner
vstinner merged commit 600f3fe into python:main Nov 18, 2025
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vstinner deleted the object_dump branch November 18, 2025 16:13
@bedevere-app bedevere-app Bot removed the awaiting merge label Nov 18, 2025
serhiy-storchaka
serhiy-storchaka reviewed Nov 18, 2025
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Comment thread Objects/object.c
_PyObject_Dump(PyObject* op)
PyUnstable_Object_Dump(PyObject* op)
{
if (_PyObject_IsFreed(op)) {

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Maybe add a special case for op == NULL?

And for type == NULL?

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@vstinner vstinner Nov 18, 2025

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It displays freed in both cases. There is now an unit test for that.

How do you suggest to format op==NULL and/or type==NULL?

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@serhiy-storchaka serhiy-storchaka Nov 18, 2025

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If this is already tested, then good. I was not sure that _PyObject_IsFreed() works with NULL (it could crash).

If type==NULL (very unlikely), then type->tp_name and repr() will crash. They will also crash if type was freed or if it is just a garbage. We could skip prints in that case avoid crash, although it may be too late.

Looking at the code, it seems the ideas I had (testing against the patterns used to fill the freed memory) was already implemented in _PyMem_IsPtrFreed().

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@vstinner vstinner Nov 18, 2025

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If type==NULL (very unlikely), then type->tp_name and repr() will crash

_PyObject_IsFreed() checks _PyMem_IsPtrFreed(Py_TYPE(op)). We just display freed in this case, without displaying tp_name or trying to call repr().

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@ZeroIntensity

ZeroIntensity commented Nov 18, 2025

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There's a bunch of unstable API like that -- I think some people would be sad to PyUnstable_Code_GetExtra go, for example.

What's the point of an unstable API that we can't remove?
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StanFromIreland pushed a commit to StanFromIreland/cpython that referenced this pull request Dec 6, 2025
@vstinner @ZeroIntensity
@kumaraditya303 @encukou @StanFromIreland
pythongh-141070: Add PyUnstable_Object_Dump() function (python#141072)
7aab25c 
* Promote _PyObject_Dump() as a public function.
* Keep _PyObject_Dump() alias to PyUnstable_Object_Dump()
  for backward compatibility.
* Replace _PyObject_Dump() with PyUnstable_Object_Dump().

Co-authored-by: Peter Bierma <[email protected]>
Co-authored-by: Kumar Aditya <[email protected]>
Co-authored-by: Petr Viktorin <[email protected]>
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@encukou encukou encukou left review comments
@serhiy-storchaka serhiy-storchaka serhiy-storchaka left review comments
@ZeroIntensity ZeroIntensity ZeroIntensity approved these changes
@kumaraditya303 kumaraditya303 kumaraditya303 approved these changes
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner
@AA-Turner AA-Turner Awaiting requested review from AA-Turner AA-Turner is a code owner

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