gh-132176: Fix crash on type() when tuple subclass passed as bases

Author: sobolevn

Lib/test/test_types.py

@@ -1819,6 +1819,19 @@ class Model(metaclass=ModelBase):
         with self.assertRaises(RuntimeWarning):
             type("SouthPonies", (Model,), {})
 
+    def test_tuple_subclass_as_bases(self):
+        # gh-132176: it used to crash on using
+        # tuple subclass for as base classes.
+        class TupleSubclass(tuple): pass
+
+        typ = type("typ", TupleSubclass((int, object)), {})
+        self.assertTrue(issubclass(typ, int))
+        self.assertTrue(issubclass(typ, object))
+        self.assertFalse(issubclass(typ, tuple))
+        self.assertIsInstance(typ(), int)
+        self.assertIsInstance(typ(), object)
+        self.assertNotIsInstance(typ(), tuple)
+
 
 class SimpleNamespaceTests(unittest.TestCase):
 

Misc/NEWS.d/next/Core_and_Builtins/2025-04-07-12-50-10.gh-issue-132176.PRDbkA.rst

@@ -0,0 +1,2 @@
+Fix a crash when :func:`type` receives a :class:`tuple` subclass as the
+second *bases* argument.

Objects/typeobject.c

@@ -497,10 +497,11 @@ _PyType_GetBases(PyTypeObject *self)
 static inline void
 set_tp_bases(PyTypeObject *self, PyObject *bases, int initial)
 {
-    assert(PyTuple_CheckExact(bases));
+    assert(PyTuple_Check(bases));
     if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
         // XXX tp_bases can probably be statically allocated for each
         // static builtin type.
+        assert(PyTuple_CheckExact(bases));
         assert(initial);
         assert(self->tp_bases == NULL);
         if (PyTuple_GET_SIZE(bases) == 0) {