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gh-145119: Allow frozendict to be assigned to instance __dict__ by mohsinm-dev · Pull Request #145123 · python/cpython · GitHub

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

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

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gh-145119: Allow frozendict to be assigned to instance __dict__
mohsinm-dev Feb 22, 2026
8013782
Update __dict__ assignment error message
mohsinm-dev Mar 5, 2026
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16 changes: 12 additions & 4 deletions Lib/test/test_capi/test_dict.py
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Original file line number Diff line number Diff line change
Expand Up @@ -273,7 +273,9 @@ def test_dict_setitem(self):
self.assertEqual(dct, {'a': 5, '\U0001f40d': 8})

self.assertRaises(TypeError, setitem, {}, [], 5) # unhashable
for test_type in NOT_DICT_TYPES + OTHER_TYPES:
for test_type in FROZENDICT_TYPES:
self.assertRaises(TypeError, setitem, test_type(), 'a', 5)
for test_type in MAPPING_TYPES + OTHER_TYPES:
self.assertRaises(SystemError, setitem, test_type(), 'a', 5)
# CRASHES setitem({}, NULL, 5)
# CRASHES setitem({}, 'a', NULL)
Expand All @@ -290,7 +292,9 @@ def test_dict_setitemstring(self):
self.assertEqual(dct, {'a': 5, '\U0001f40d': 8})

self.assertRaises(UnicodeDecodeError, setitemstring, {}, INVALID_UTF8, 5)
for test_type in NOT_DICT_TYPES + OTHER_TYPES:
for test_type in FROZENDICT_TYPES:
self.assertRaises(TypeError, setitemstring, test_type(), b'a', 5)
for test_type in MAPPING_TYPES + OTHER_TYPES:
self.assertRaises(SystemError, setitemstring, test_type(), b'a', 5)
# CRASHES setitemstring({}, NULL, 5)
# CRASHES setitemstring({}, b'a', NULL)
Expand All @@ -308,7 +312,9 @@ def test_dict_delitem(self):
self.assertEqual(dct, {'c': 2})

self.assertRaises(TypeError, delitem, {}, []) # unhashable
for test_type in NOT_DICT_TYPES:
for test_type in FROZENDICT_TYPES:
self.assertRaises(TypeError, delitem, test_type({'a': 1}), 'a')
for test_type in MAPPING_TYPES:
self.assertRaises(SystemError, delitem, test_type({'a': 1}), 'a')
for test_type in OTHER_TYPES:
self.assertRaises(SystemError, delitem, test_type(), 'a')
Expand All @@ -327,7 +333,9 @@ def test_dict_delitemstring(self):
self.assertEqual(dct, {'c': 2})

self.assertRaises(UnicodeDecodeError, delitemstring, {}, INVALID_UTF8)
for test_type in NOT_DICT_TYPES:
for test_type in FROZENDICT_TYPES:
self.assertRaises(TypeError, delitemstring, test_type({'a': 1}), b'a')
for test_type in MAPPING_TYPES:
self.assertRaises(SystemError, delitemstring, test_type({'a': 1}), b'a')
for test_type in OTHER_TYPES:
self.assertRaises(SystemError, delitemstring, test_type(), b'a')
Expand Down
39 changes: 39 additions & 0 deletions Lib/test/test_descr.py
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Expand Up @@ -3570,6 +3570,45 @@ class Exception2(Base, Exception):
self.assertEqual(e.a, 1)
self.assertEqual(can_delete_dict(e), can_delete_dict(ValueError()))

def test_set_dict_to_frozendict(self):
# gh-145119: __dict__ accepts frozendict.
class C:
pass

obj = C()
obj.__dict__ = frozendict(x=1, y=2)
self.assertEqual(obj.x, 1)
self.assertEqual(obj.y, 2)
self.assertIn("x", dir(obj))
self.assertIn("y", dir(obj))
self.assertEqual(type(vars(obj)), frozendict)

with self.assertRaises(TypeError):
obj.z = 3
with self.assertRaises(TypeError):
del obj.x

class MyFrozenDict(frozendict):
pass

obj.__dict__ = MyFrozenDict(a=10)
self.assertEqual(obj.a, 10)
self.assertIn("a", dir(obj))

obj.__dict__ = {"w": 50}
obj.q = 99
self.assertEqual(obj.q, 99)

# Ensure internal PyDict_SetItem/DelItem paths raise TypeError,
# not SystemError, when __dict__ is a frozendict.
cm = classmethod(lambda: None)
cm.__dict__ = frozendict()
with self.assertRaises(TypeError):
cm.__annotations__ = {"x": int}
cm.__dict__ = frozendict(__annotations__={"x": int})
with self.assertRaises(TypeError):
del cm.__annotations__

def test_binary_operator_override(self):
# Testing overrides of binary operations...
class I(int):
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-02-22-23-50-00.gh-issue-145119.hN4sQ8.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Allow :class:`frozendict` to be assigned to an instance's
:attr:`~object.__dict__`, enabling immutable instances.
21 changes: 21 additions & 0 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2743,6 +2743,11 @@ int
PyDict_SetItem(PyObject *op, PyObject *key, PyObject *value)
{
if (!PyDict_Check(op)) {
if (PyFrozenDict_Check(op)) {
PyErr_SetString(PyExc_TypeError,
"'frozendict' object does not support item assignment");
return -1;
}
PyErr_BadInternalCall();
return -1;
}
Expand Down Expand Up @@ -2883,6 +2888,11 @@ _PyDict_DelItem_KnownHash_LockHeld(PyObject *op, PyObject *key, Py_hash_t hash)
PyObject *old_value;

if (!PyDict_Check(op)) {
if (PyFrozenDict_Check(op)) {
PyErr_SetString(PyExc_TypeError,
"'frozendict' object does not support item deletion");
return -1;
}
PyErr_BadInternalCall();
return -1;
}
Expand Down Expand Up @@ -7064,6 +7074,17 @@ int
_PyDict_SetItem_LockHeld(PyDictObject *dict, PyObject *name, PyObject *value)
{
if (!PyDict_Check(dict)) {
if (PyFrozenDict_Check((PyObject *)dict)) {
if (value == NULL) {
PyErr_SetString(PyExc_TypeError,
"'frozendict' object does not support item deletion");
}
else {
PyErr_SetString(PyExc_TypeError,
"'frozendict' object does not support item assignment");
}
return -1;
}
PyErr_BadInternalCall();
return -1;
}
Expand Down
25 changes: 17 additions & 8 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3999,10 +3999,10 @@ subtype_dict(PyObject *obj, void *context)
int
_PyObject_SetDict(PyObject *obj, PyObject *value)
{
if (value != NULL && !PyDict_Check(value)) {
if (value != NULL && !PyAnyDict_Check(value)) {

chatgpt-codex-connector Bot Feb 22, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

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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PyErr_Format(PyExc_TypeError,
"__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);
return -1;
}
if (Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
Expand Down Expand Up @@ -8305,15 +8305,24 @@ object___dir___impl(PyObject *self)
if (dict == NULL) {
dict = PyDict_New();
}
else if (!PyDict_Check(dict)) {
Py_DECREF(dict);
dict = PyDict_New();
}
else {
else if (PyDict_Check(dict)) {
/* Copy __dict__ to avoid mutating it. */
PyObject *temp = PyDict_Copy(dict);
Py_SETREF(dict, temp);
}
else if (PyFrozenDict_Check(dict)) {
/* Convert frozendict to a mutable dict for merging. */

vstinner Mar 5, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Please wait for #145517. If PyDict_Copy() is modified to always return a dict, you can reuse the PyDict_Check() branch for frozendict.

vstinner Mar 5, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

For now, you can use _PyDict_CopyAsDict() from Include/internal/pycore_dict.h.
PyObject *temp = PyDict_New();
if (temp != NULL && PyDict_Update(temp, dict) < 0) {
Py_DECREF(temp);
temp = NULL;
}
Py_SETREF(dict, temp);
}
else {
Py_DECREF(dict);
dict = PyDict_New();
}

if (dict == NULL)
goto error;
Expand Down
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