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gh-145119: Allow frozendict to be assigned to instance __dict__#145123

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mohsinm-dev:gh-145119-frozendict-instance-dict
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gh-145119: Allow frozendict to be assigned to instance __dict__#145123
mohsinm-dev wants to merge 1 commit intopython:mainfrom
mohsinm-dev:gh-145119-frozendict-instance-dict

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@mohsinm-dev mohsinm-dev commented Feb 22, 2026

Allow frozendict (and its subclasses) to be assigned to an instance's __dict__, enabling immutable instances.

Changes:

  • _PyObject_SetDict: accept frozendict via PyAnyDict_Check
  • _PyDict_SetItem_LockHeld: raise TypeError on set/delete instead of SystemError
  • object___dir___impl: convert frozendict to a mutable dict for merging

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Reviewed commit: 6b702cf72b

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_PyObject_SetDict(PyObject *obj, PyObject *value)
{
if (value != NULL && !PyDict_Check(value)) {
if (value != NULL && !PyAnyDict_Check(value)) {

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P2 Badge Avoid frozendict dict on objects mutating their own dict

Allowing _PyObject_SetDict() to accept PyAnyDict_Check here makes frozendict assignable to every PyObject_GenericSetDict user, but some of those types still perform internal writes with PyDict_SetItem/PyDict_DelItem (for example descriptor_get_wrapped_attribute and descriptor_set_wrapped_attribute in Objects/funcobject.c for classmethod/staticmethod annotation caching). PyDict_SetItem still rejects frozendict with PyErr_BadInternalCall, so after obj.__dict__ = frozendict(...), operations like reading or updating __annotations__ can now raise SystemError instead of behaving normally or reporting an intentional immutability error.

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@mohsinm-dev mohsinm-dev force-pushed the gh-145119-frozendict-instance-dict branch from 6b702cf to 8d6ec8d Compare February 22, 2026 19:22
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In order to keep the commit history intact, please avoid squashing or amending history and then force-pushing to the PR. Reviewers often want to look at individual commits. When the PR is merged, everything will be squashed into a single commit.

Py_SETREF(dict, temp);
}
else if (PyFrozenDict_Check(dict)) {
/* Convert frozendict to a mutable dict for merging. */
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Please wait for #145517. If PyDict_Copy() is modified to always return a dict, you can reuse the PyDict_Check() branch for frozendict.

Comment on lines 4004 to 4005
"__dict__ must be set to a dictionary, "
"not a '%.200s'", Py_TYPE(value)->tp_name);
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Suggested change
"__dict__ must be set to a dictionary, "
"not a '%.200s'", Py_TYPE(value)->tp_name);
"__dict__ must be set to a dict or frozendict, "
"not a %T", value);

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3 participants