gh-86069: Do not ignore the third argument in slot_nb_inplace_power()

Lib/test/test_capi/test_number.py

@@ -248,8 +248,7 @@ def __ipow__(*args):
 
         x = X()
         self.assertEqual(inplacepower(x, 11), (x, 11))
-        # XXX: In-place power doesn't pass the third arg to __ipow__.
-        self.assertEqual(inplacepower(x, 11, 5), (x, 11))
+        self.assertEqual(inplacepower(x, 11, 5), (x, 11, 5))
 
     def test_long(self):
         # Test PyNumber_Long()

Misc/NEWS.d/next/Core_and_Builtins/2025-02-17-15-04-19.gh-issue-86069.qeWCJF.rst

@@ -0,0 +1,4 @@
+The default implementation of the
+:c:member:`~PyNumberMethods.nb_inplace_power` slot no longer ignores the
+third argument, but passes it to the :meth:`~object.__ipow__` method if its
+value is not ``None``.

Objects/typeobject.c

@@ -9907,8 +9907,14 @@ SLOT1(slot_nb_inplace_remainder, __imod__, PyObject *)
 static PyObject *
 slot_nb_inplace_power(PyObject *self, PyObject * arg1, PyObject *arg2)
 {
-    PyObject *stack[2] = {self, arg1};
-    return vectorcall_method(&_Py_ID(__ipow__), stack, 2);
+    if (arg2 == Py_None) {
+        PyObject *stack[2] = {self, arg1};
+        return vectorcall_method(&_Py_ID(__ipow__), stack, 2);
+    }
+    else {
+        PyObject *stack[3] = {self, arg1, arg2};
+        return vectorcall_method(&_Py_ID(__ipow__), stack, 3);
+    }
 }
 SLOT1(slot_nb_inplace_lshift, __ilshift__, PyObject *)
 SLOT1(slot_nb_inplace_rshift, __irshift__, PyObject *)