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GeezerVison is showing github.com — gh-145876: preserve AttributeError in dict unpacking by zakiscoding · Pull Request #145878 · python/cpython

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@zakiscoding

@zakiscoding zakiscoding commented Mar 12, 2026 •
edited by bedevere-app Bot
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Summary\n- preserve AttributeError raised from mapping methods during dict unpacking\n- keep TypeError for objects that are not mappings\n- add a regression test in test_unpack_ex\n\n## Testing\n- PCbuild\build.bat -p x64 -c Release\n- PCbuild\amd64\python.exe -m test -v test_unpack_ex\n\nCloses #145876

  • Issue: AttributeErrors raised in .keys() or .__getitem__() during {**mymapping}are incorrectly masked #145876

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@zakiscoding
pythongh-145876: preserve AttributeError in dict unpacking
8a2bab8
@zakiscoding
zakiscoding requested a review from markshannon as a code owner March 12, 2026 20:10
Copilot AI review requested due to automatic review settings March 12, 2026 20:10
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python-cla-bot Bot commented Mar 12, 2026 •
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@bedevere-app

bedevere-app Bot commented Mar 12, 2026

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Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.
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@bedevere-app bedevere-app Bot mentioned this pull request Mar 12, 2026
AttributeErrors raised in .keys() or .__getitem__() during {**mymapping}are incorrectly masked #145876
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@bedevere-app bedevere-app Bot added the awaiting review label Mar 12, 2026
@picnixz picnixz closed this Mar 12, 2026
Copilot started reviewing on behalf of zakiscoding March 12, 2026 20:11
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Pull request overview

This PR adjusts dict-unpacking ({**obj} / DICT_UPDATE) error handling so that AttributeError raised from within a mapping’s keys() / __getitem__ is propagated, instead of being incorrectly rewritten as TypeError: '... object is not a mapping'.

Changes:

  • Update DICT_UPDATE to only convert AttributeError into “not a mapping” when update_o truly lacks a keys attribute; otherwise restore and propagate the original exception.
  • Regenerate the tier-1 interpreter cases to include the updated error-handling logic.
  • Add doctest coverage ensuring AttributeError from keys() / __getitem__ is preserved during dict unpacking.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File Description
Python/generated_cases.c.h Regenerated tier-1 interpreter DICT_UPDATE case to preserve AttributeError from mapping internals.
Python/bytecodes.c Updates the DICT_UPDATE bytecode definition’s error translation logic.
Lib/test/test_unpack_ex.py Adds doctests to ensure {**obj} propagates AttributeError raised by keys() / __getitem__.

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Comment thread Python/bytecodes.c
Comment on lines +2247 to +2251
PyObject *exc = PyErr_GetRaisedException();
PyObject *keys = NULL;
int has_keys = PyObject_GetOptionalAttr(update_o, &_Py_ID(keys), &keys);

if (has_keys < 0) {

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DICT_UPDATE now preserves the original AttributeError only when update_o has a keys attribute, but the tier-2 interpreter (Python/executor_cases.c.h) is generated from bytecodes.c and currently still contains the old unconditional conversion of AttributeError into TypeError. This will make behavior differ between tier-1 and tier-2 execution (and can break the new tests when tier-2 is enabled). Please regenerate/update the tier-2 cases so DICT_UPDATE matches this new logic everywhere.

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@picnixz

picnixz commented Mar 12, 2026

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Note that LLM-generated PRs are not accepted unless acknlowedge and properly reviewed. Read https://devguide.python.org/getting-started/generative-ai/ before opening other PRs please.
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@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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3 participants

@zakiscoding @picnixz
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