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gh-145876: preserve AttributeError in dict unpacking#145878

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gh-145876: preserve AttributeError in dict unpacking #145878

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23 changes: 23 additions & 0 deletions Lib/test/test_unpack_ex.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -134,6 +134,29 @@
...
TypeError: 'list' object is not a mapping

>>> class MappingWithKeyErrors:
... def __init__(self, *, keys_error=None, getitem_error=None):
... self.keys_error = keys_error
... self.getitem_error = getitem_error
... def keys(self):
... if self.keys_error is not None:
... raise self.keys_error("error in keys")
... return [1, 2, 3]
... def __getitem__(self, key):
... if self.getitem_error is not None:
... raise self.getitem_error("error in __getitem__")
... return key * 2

>>> {**MappingWithKeyErrors(keys_error=AttributeError)}
Traceback (most recent call last):
...
AttributeError: error in keys

>>> {**MappingWithKeyErrors(getitem_error=AttributeError)}
Traceback (most recent call last):
...
AttributeError: error in __getitem__

>>> len(eval("{" + ", ".join("**{{{}: {}}}".format(i, i)
... for i in range(1000)) + "}"))
1000
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21 changes: 18 additions & 3 deletions Python/bytecodes.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2244,9 +2244,24 @@ dummy_func(
if (err < 0) {
int matches = _PyErr_ExceptionMatches(tstate, PyExc_AttributeError);
if (matches) {
_PyErr_Format(tstate, PyExc_TypeError,
"'%.200s' object is not a mapping",
Py_TYPE(update_o)->tp_name);
PyObject *exc = PyErr_GetRaisedException();
PyObject *keys = NULL;
int has_keys = PyObject_GetOptionalAttr(update_o, &_Py_ID(keys), &keys);

if (has_keys < 0) {
Comment on lines +2247 to +2251

CopilotAIMar 12, 2026

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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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Py_XDECREF(keys);
Py_DECREF(exc);
}
else if (has_keys == 0) {
Py_DECREF(exc);
_PyErr_Format(tstate, PyExc_TypeError,
"'%.200s' object is not a mapping",
Py_TYPE(update_o)->tp_name);
}
else {
Py_DECREF(keys);
PyErr_SetRaisedException(exc);
}
}
PyStackRef_CLOSE(update);
ERROR_IF(true);
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28 changes: 25 additions & 3 deletions Python/generated_cases.c.h
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