gh-155181: Untrack frozensets created from set literals when possible

Author: aisk

Lib/test/test_set.py

@@ -762,6 +762,17 @@ def test_constructor_identity(self):
         t = self.thetype(s)
         self.assertEqual(id(s), id(t))
 
+    def test_gc_tracking(self):
+        # gh-140232: frozensets whose elements can never be tracked by the
+        # GC are not tracked, including the compiled frozenset({...}) form
+        s = {1, 2}
+        self.assertFalse(gc.is_tracked(frozenset(s)))
+        self.assertFalse(gc.is_tracked(frozenset({1, 2})))
+        self.assertFalse(gc.is_tracked(frozenset({x for x in range(2)})))
+        class C:
+            pass
+        self.assertTrue(gc.is_tracked(frozenset({C()})))
+
     def test_hash(self):
         self.assertEqual(hash(self.thetype('abcdeb')),
                          hash(self.thetype('ebecda')))

Misc/NEWS.d/next/Core_and_Builtins/2026-08-05-01-10-20.gh-issue-155181.jj8jhk.rst

@@ -0,0 +1,3 @@
+:class:`frozenset` objects created from a set literal or a set comprehension
+are now untracked by the garbage collector when none of their elements can
+be tracked.

Objects/setobject.c

@@ -1574,6 +1574,7 @@ _PySet_Freeze(PyObject *set)
     assert(PySet_CheckExact(set));
     assert(_PyObject_IsUniquelyReferenced(set));
     set->ob_type = &PyFrozenSet_Type;
+    _PyFrozenSet_MaybeUntrack(set);
     return Py_NewRef(set);
 }