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gh-151672: Treat string fromlist like __import__ for lazy imports #152322

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gh-151672: Treat string fromlist like __import__ for lazy imports #152322

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929272e
gh-152235: Defer GC tracking until set_init completes on tp_new path
sourabhligade Jun 26, 2026
d8615cb
gh-151672: Treat string fromlist like __import__ for lazy imports
sourabhligade Jun 26, 2026
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38 changes: 27 additions & 11 deletions Objects/setobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1483,7 +1483,11 @@ frozenset_vectorcall(PyObject *type, PyObject * const*args,
static PyObject *
set_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
return make_new_set(type, NULL);
/* Leave GC-untracked until set_init() finishes filling (gh-152235).
* The vectorcall path uses make_new_set() and tracks at the end; the
* classic tp_new/tp_init path must do the same so a half-built set is
* never visible to gc.get_objects() / another thread during __init__. */
return make_new_set_untracked(type, NULL);
}

#ifdef Py_GIL_DISABLED
Expand Down Expand Up @@ -2750,6 +2754,7 @@ set_init(PyObject *so, PyObject *args, PyObject *kwds)
{
PySetObject *self = _PySet_CAST(so);
PyObject *iterable = NULL;
int rv;

if (!_PyArg_NoKeywords("set", kwds))
return -1;
Expand All @@ -2759,19 +2764,30 @@ set_init(PyObject *so, PyObject *args, PyObject *kwds)
if (_PyObject_IsUniquelyReferenced((PyObject *)self) && self->fill == 0) {
self->hash = -1;
if (iterable == NULL) {
return 0;
rv = 0;
}
else {
rv = set_update_local(self, iterable);
}
return set_update_local(self, iterable);
}
Py_BEGIN_CRITICAL_SECTION(self);
if (self->fill)
set_clear_internal((PyObject*)self);
self->hash = -1;
Py_END_CRITICAL_SECTION();
else {
Py_BEGIN_CRITICAL_SECTION(self);
if (self->fill)
set_clear_internal((PyObject*)self);
self->hash = -1;
Py_END_CRITICAL_SECTION();

if (iterable == NULL)
return 0;
return set_update_internal(self, iterable);
if (iterable == NULL)
rv = 0;
else
rv = set_update_internal(self, iterable);
}

/* Track only once fully built (pairs with set_new leaving it untracked). */
if (rv == 0 && !_PyObject_GC_IS_TRACKED(so)) {
_PyObject_GC_TRACK(so);
}
return rv;
}

static PyObject*
Expand Down
21 changes: 15 additions & 6 deletions Python/import.c
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Original file line number Diff line number Diff line change
Expand Up @@ -4567,8 +4567,22 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
}
}

// Match __import__: a string fromlist is a sequence of names, not a
// single attribute. Normalize to a 1-tuple so resolve() returns the
// module (gh-151672).
PyObject *fromlist_owned = NULL;
if (fromlist != NULL && PyUnicode_Check(fromlist)) {
fromlist_owned = PyTuple_Pack(1, fromlist);
if (fromlist_owned == NULL) {
Py_DECREF(abs_name);
return NULL;
}
fromlist = fromlist_owned;
}

// here, 'filter' is either NULL or is equivalent to a borrowed reference
PyObject *res = _PyLazyImport_New(frame, builtins, abs_name, fromlist);
Py_XDECREF(fromlist_owned);
if (res == NULL) {
Py_DECREF(abs_name);
return NULL;
Expand All @@ -4580,12 +4594,7 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
goto error;
}

if (fromlist && PyUnicode_Check(fromlist)) {
if (register_from_lazy_on_parent(tstate, abs_name, fromlist) < 0) {
goto error;
}
}
else if (fromlist && PyTuple_Check(fromlist) &&
if (fromlist && PyTuple_Check(fromlist) &&
PyTuple_GET_SIZE(fromlist)) {
for (Py_ssize_t i = 0; i < PyTuple_GET_SIZE(fromlist); i++) {
if (register_from_lazy_on_parent(tstate, abs_name,
Expand Down