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gh-151722: Do not track the dict in the GC in _PyDict_FromKeys() #152067

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gh-151722: Do not track the dict in the GC in _PyDict_FromKeys() #152067

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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-06-24-13-36-31.gh-issue-151722.lWKfE1.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:meth:`!frozendict.fromkeys` now creates a :class:`frozendict` which is not
tracked by the garbage collector, and only tracks it once the dictionary is
fully initialized. Patch by Donghee Na and Victor Stinner.
84 changes: 54 additions & 30 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -140,6 +140,7 @@ static PyObject* frozendict_new(PyTypeObject *type, PyObject *args,
PyObject *kwds);
static PyObject* frozendict_new_untracked(PyTypeObject *type);
static PyObject* dict_new(PyTypeObject *type, PyObject *args, PyObject *kwds);
static PyObject* dict_new_untracked(PyTypeObject *type);
static int dict_merge(PyObject *a, PyObject *b, int override, PyObject **dupkey);
static int dict_contains(PyObject *op, PyObject *key);
static int dict_merge_from_seq2(PyObject *d, PyObject *seq2, int override);
Expand Down Expand Up @@ -3414,40 +3415,49 @@ dict_set_fromkeys(PyDictObject *mp, PyObject *iterable, PyObject *value)
PyObject *
_PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
{
PyObject *it; /* iter(iterable) */
PyObject *it = NULL; /* iter(iterable) */
PyObject *key;
PyObject *d;
int status;

d = _PyObject_CallNoArgs(cls);
PyTypeObject *cls_type = _PyType_CAST(cls);
if (PyObject_IsSubclass(cls, (PyObject*)&PyFrozenDict_Type)
&& cls_type->tp_new == frozendict_new)
{
// gh-151722: Create a frozendict copy which is not tracked by the GC.
d = frozendict_new_untracked(cls_type);
}
else {
d = _PyObject_CallNoArgs(cls);
}
if (d == NULL) {
return NULL;
}

// If cls is a dict or frozendict subclass with overridden constructor,
// copy the frozendict.
PyTypeObject *cls_type = _PyType_CAST(cls);
if (PyFrozenDict_Check(d) && cls_type->tp_new != frozendict_new) {
// gh-151722: If cls constructor returns a frozendict which is tracked by
// the GC, create a frozendict copy which is not tracked by the GC.
if (PyFrozenDict_Check(d) && _PyObject_GC_IS_TRACKED(d)) {
// Subclass-friendly copy
PyObject *copy;
if (PyObject_IsSubclass(cls, (PyObject*)&PyFrozenDict_Type)) {
copy = frozendict_new(cls_type, NULL, NULL);
copy = frozendict_new_untracked(cls_type);
}
else {
copy = dict_new(cls_type, NULL, NULL);
copy = dict_new_untracked(cls_type);
}
if (copy == NULL) {
Py_DECREF(d);
return NULL;
goto Fail;
}
if (dict_merge(copy, d, 1, NULL) < 0) {
Py_DECREF(d);
Py_DECREF(copy);
return NULL;
goto Fail;
}
Py_SETREF(d, copy);
}
assert(!PyFrozenDict_Check(d) || can_modify_dict((PyDictObject*)d));
if (PyFrozenDict_Check(d)) {
assert(!_PyObject_GC_IS_TRACKED(d));
}

if (PyDict_CheckExact(d)) {
if (PyDict_CheckExact(iterable)) {
Expand All @@ -3456,23 +3466,23 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
Py_BEGIN_CRITICAL_SECTION2(d, iterable);
d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
Py_END_CRITICAL_SECTION2();
return d;
goto Done;
}
else if (PyFrozenDict_CheckExact(iterable)) {
PyDictObject *mp = (PyDictObject *)d;

Py_BEGIN_CRITICAL_SECTION(d);
d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
Py_END_CRITICAL_SECTION();
return d;
goto Done;
}
else if (PyAnySet_CheckExact(iterable)) {
PyDictObject *mp = (PyDictObject *)d;

Py_BEGIN_CRITICAL_SECTION2(d, iterable);
d = (PyObject *)dict_set_fromkeys(mp, iterable, value);
Py_END_CRITICAL_SECTION2();
return d;
goto Done;
}
}
else if (PyFrozenDict_CheckExact(d)) {
Expand All @@ -3482,27 +3492,26 @@ _PyDict_FromKeys(PyObject *cls, PyObject *iterable, PyObject *value)
Py_BEGIN_CRITICAL_SECTION(iterable);
d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
Py_END_CRITICAL_SECTION();
return d;
goto Done;
}
else if (PyFrozenDict_CheckExact(iterable)) {
PyDictObject *mp = (PyDictObject *)d;
d = (PyObject *)dict_dict_fromkeys(mp, iterable, value);
return d;
goto Done;
}
else if (PyAnySet_CheckExact(iterable)) {
PyDictObject *mp = (PyDictObject *)d;

Py_BEGIN_CRITICAL_SECTION(iterable);
d = (PyObject *)dict_set_fromkeys(mp, iterable, value);
Py_END_CRITICAL_SECTION();
return d;
goto Done;
}
}

it = PyObject_GetIter(iterable);
if (it == NULL){
Py_DECREF(d);
return NULL;
goto Fail;
}

if (PyDict_CheckExact(d)) {
Expand Down Expand Up @@ -3541,12 +3550,19 @@ dict_iter_exit:;
if (PyErr_Occurred())
goto Fail;
Py_DECREF(it);
return d;
goto Done;

Fail:
Py_DECREF(it);
Py_XDECREF(it);
Py_DECREF(d);
return NULL;

Done:
// d can be NULL
if (d != NULL && !_PyObject_GC_IS_TRACKED(d)) {
_PyObject_GC_TRACK(d);
}
return d;
}

/* Methods */
Expand Down Expand Up @@ -4147,9 +4163,6 @@ dict_dict_merge(PyDictObject *mp, PyDictObject *other, int override, PyObject **
set_keys(mp, keys);
STORE_USED(mp, other->ma_used);
ASSERT_CONSISTENT(mp);
if (PyDict_Check(mp)) {
assert(_PyObject_GC_IS_TRACKED(mp));
}
return 0;
}
}
Expand Down Expand Up @@ -4316,7 +4329,12 @@ dict_merge_api(PyObject *a, PyObject *b, int override, PyObject **dupkey)
}
return -1;
}
return dict_merge(a, b, override, dupkey);

int res = dict_merge(a, b, override, dupkey);
if (PyDict_Check(a)) {
assert(_PyObject_GC_IS_TRACKED(a));
}
return res;
}

int
Expand Down Expand Up @@ -4475,10 +4493,16 @@ copy_lock_held(PyObject *o, int as_frozendict)
}
if (copy == NULL)
return NULL;
if (dict_merge(copy, o, 1, NULL) == 0)
return copy;
Py_DECREF(copy);
return NULL;
if (dict_merge(copy, o, 1, NULL) < 0) {
Py_DECREF(copy);
return NULL;

}

if (PyDict_Check(copy)) {
assert(_PyObject_GC_IS_TRACKED(copy));
}
return copy;
}

PyObject *
Expand Down
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