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gh-144989: Expose special method lookup at Python level - #144990

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tanloong wants to merge 33 commits into
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tanloong:expose-lookupspeicalmethod
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gh-144989: Expose special method lookup at Python level#144990
tanloong wants to merge 33 commits into
python:mainfrom
tanloong:expose-lookupspeicalmethod

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@tanloongtanloong commented Feb 19, 2026•
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This exposes _PyObject_LookupSpecialMethod() as types.lookup_special_method(obj, attr).

I am not quite sure which one between the two similar funtions in Objects/typeobject.c should be preferred to be exposed: _PyObject_LookupSpecial() or _PyObject_LookupSpecialMethod(). I chose the _PyObject_LookupSpecialMethod() because it is the function that is called by LOAD_SPECIAL. So I suppose using this one is more consistent with the CPython interpreter when parsing with-statements (#144386 (comment)).

However, I am open to adjusting the PR to expose _PyObject_LookupSpecial() instead if that one is more suitable.

Updated based on the consensus reached by now on discourse discussion:

  1. Switched to _PyObject_LookupSpecial instead of _PyObject_LookupSpecialMethod and accordingly renamed (for now) the function from lookup_special_method to lookup_special.
  2. Raise AttributeError if the special method is not found.
  3. Add optional default parameter similar to getattr.

📚 Documentation preview 📚: https://cpython-previews--144990.org.readthedocs.build/

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This needs a "What's New in Python 3.15" entry.

Comment threadModules/_typesmodule.c
Comment threadModules/_typesmodule.c Outdated
Comment threadModules/_typesmodule.c Outdated
Comment threadDoc/library/types.rst Outdated
Comment threadDoc/library/types.rst Outdated
Comment threadMisc/NEWS.d/next/Library/2026-02-19-17-46-59.gh-issue-144989.JAuJyG.rst Outdated
Comment threadModules/_typesmodule.c
@tanloong

tanloong commented Feb 19, 2026

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@ZeroIntensity Thank you for your review! I've updated the code accordingly. Could you please take another look when you have time? Thanks again!

@tanloong
tanloong marked this pull request as draft February 21, 2026 12:09
@tanloong
1. expose _PyObject_LookupSpecial instead of _PyObject_LookupSpecialM…
671185e
…ethod;
2. raise AttributeError instead of returning None;
3. add optional `default` parameter, similar to `getattr`: lookup_special(object, name[, default])
4. There are different opinions on which module should the function be
in. Leave it in `types` until there is consensus.
@tanloong
fix signature error in test_inspect.py
98735f6
This is temporary as which module should the function be put is not determined yet in the discourse discussion.
@tanloong
fix whatsnew
f0f26e4
This is temporary as which module should the function be put is not determined yet in the discourse discussion.
@tanloong
Merge branch 'main' into expose-lookupspeicalmethod
10ff83f
tanloongand others added 2 commits February 23, 2026 22:22
@tanloong@JoBeGaming
Addeddefaultparameter tolookup_specialintypes.py(#5)
9f66dc9
* Added `default` parameter to `lookup_special` in `types.py`
See https://discuss.python.org/t/expose-special-method-lookup-at-python-level/106236 for more.
---------
Co-authored-by: JoBe <165585785+JoBeGaming@users.noreply.github.com>
@JoBeGaming
Removed duplicated definition oflookup_specialintypes.py. (#6)
5cf9c4c
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All commit authors signed the Contributor License Agreement.

CLA signed

@tanloongtanloong mentioned this pull request Feb 23, 2026
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@JoBeGaming

JoBeGaming commented Feb 23, 2026

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Finally all checks passing :)

tanloongand others added 2 commits February 28, 2026 00:14
@tanloong@JoBeGaming
Added positional-only marker in lookup_special definition (#8)
74457bf
Co-authored-by: JoBe <165585785+JoBeGaming@users.noreply.github.com>
@tanloong
add Argument Clinic comment
4ca90bf
This line of comment is copied from definition of `builtin_getattr` in
Python/bltinmodule.c. Make this newly added `_types_lookup_special_impl`
easier to be found when doing the Argument Clinic convertion in the future.
@tanloong
tanloong marked this pull request as ready for review March 1, 2026 15:39
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read-the-docs-communityBot commented May 1, 2026•
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Documentation build overview

📚 cpython-previews | 🛠️ Build #32509439 | 📁 Comparing f6c88dc against main (8066db5)

🔍 Preview build

32 files changed · ± 32 modified

±Modified

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This PR is stale because it has been open for 90 days with no activity.

@github-actionsgithub-actionsBot added the stale Stale PR or inactive for long period of time. label Aug 9, 2026
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@tanloong@JoBeGaming@ZeroIntensity