gh-161968: Fall back to the right operand's sq_repeat in PyNumber_InPlaceMultiply

Lib/test/test_augassign.py

@@ -64,6 +64,25 @@ def testSequences(self):
         self.assertEqual(x, [1, 2, 1, 2, 3])
         self.assertTrue(x is y)
 
+    def testSequenceRepeatRightOperand(self):
+        # gh-161968
+        class MyInt(int):
+            pass
+        class Index:
+            def __index__(self):
+                return 2
+
+        seq = [1]
+        x = MyInt(2)
+        x *= seq
+        self.assertEqual(x, [1, 1])
+        # The right operand is not modified in place.
+        self.assertEqual(seq, [1])
+
+        x = Index()
+        x *= 'a'
+        self.assertEqual(x, 'aa')
+
     def testCustomMethods1(self):
 
         class aug_test:

Misc/NEWS.d/next/Core_and_Builtins/2026-11-13-00-00-00.gh-issue-161968.ytuf5z.rst

@@ -0,0 +1,2 @@
+Fix ``x *= seq`` raising :exc:`TypeError` when ``x`` is an instance of an
+:class:`int` subclass or of a class defining :meth:`~object.__index__`.

Objects/abstract.c

@@ -1344,7 +1344,7 @@ PyNumber_InPlaceMultiply(PyObject *v, PyObject *w)
             if (f != NULL)
                 return sequence_repeat(f, v, w);
         }
-        else if (mw != NULL) {
+        if (mw != NULL) {
             /* Note that the right hand operand should not be
              * mutated in this case so sq_inplace_repeat is not
              * used. */