From 6da6044da94f770956cffc9c7f11c34105daa713 Mon Sep 17 00:00:00 2001
From: Kumar Aditya <kumaraditya@python.org>
Date: Thu, 17 Sep 2026 14:51:36 +0530
Subject: [PATCH] Call __instancecheck__ and __subclasscheck__ without creating
 a bound method

---
 Objects/abstract.c | 79 +++++++++++++++++++++++++++-------------------
 1 file changed, 47 insertions(+), 32 deletions(-)

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 28f751965f36b9..502807c0ac13f0 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -9,6 +9,7 @@
 #include "pycore_list.h"          // _PyList_AppendTakeRef()
 #include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_object.h"        // _Py_CheckSlotResult()
+#include "pycore_stackref.h"      // _PyStackRef
 #include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
 #include "pycore_pyerrors.h"      // _PyErr_Occurred()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
@@ -2635,6 +2636,40 @@ object_isinstance(PyObject *inst, PyObject *cls)
     return retval;
 }
 
+static int
+call_special_method(PyThreadState *tstate, PyObject *cls, PyObject *name,
+                    const char *where, PyObject *arg, PyObject **res)
+{
+    _PyCStackRef cref;
+    _PyThreadState_PushCStackRef(tstate, &cref);
+    _PyStackRef method_and_self[2] = {
+        PyStackRef_NULL, PyStackRef_FromPyObjectBorrow(cls)
+    };
+    int found = _PyObject_LookupSpecialMethod(name, method_and_self);
+    cref.ref = method_and_self[0];
+    if (found > 0) {
+        *res = NULL;
+        if (!_Py_EnterRecursiveCallTstate(tstate, where)) {
+            PyObject *method = PyStackRef_AsPyObjectBorrow(cref.ref);
+            PyObject *args[2] = {PyStackRef_AsPyObjectBorrow(method_and_self[1]), arg};
+            if (args[0] != NULL) {
+                /* Unbound method: prepend self. */
+                *res = PyObject_Vectorcall(method, args, 2, NULL);
+            }
+            else {
+                *res = PyObject_Vectorcall(method, args + 1, 1, NULL);
+            }
+            _Py_LeaveRecursiveCallTstate(tstate);
+        }
+        if (*res == NULL) {
+            found = -1;
+        }
+    }
+    PyStackRef_XCLOSE(method_and_self[1]);
+    _PyThreadState_PopCStackRef(tstate, &cref);
+    return found;
+}
+
 static int
 object_recursive_isinstance(PyThreadState *tstate, PyObject *inst, PyObject *cls)
 {
@@ -2672,26 +2707,16 @@ object_recursive_isinstance(PyThreadState *tstate, PyObject *inst, PyObject *cls
         return r;
     }
 
-    PyObject *checker = _PyObject_LookupSpecial(cls, &_Py_ID(__instancecheck__));
-    if (checker != NULL) {
-        if (_Py_EnterRecursiveCallTstate(tstate, " in __instancecheck__")) {
-            Py_DECREF(checker);
-            return -1;
-        }
-
-        PyObject *res = PyObject_CallOneArg(checker, inst);
-        _Py_LeaveRecursiveCallTstate(tstate);
-        Py_DECREF(checker);
-
-        if (res == NULL) {
-            return -1;
-        }
+    PyObject *res;
+    int found = call_special_method(tstate, cls, &_Py_ID(__instancecheck__),
+                                    " in __instancecheck__", inst, &res);
+    if (found > 0) {
         int ok = PyObject_IsTrue(res);
         Py_DECREF(res);
 
         return ok;
     }
-    else if (_PyErr_Occurred(tstate)) {
+    else if (found < 0) {
         return -1;
     }
 
@@ -2731,8 +2756,6 @@ recursive_issubclass(PyObject *derived, PyObject *cls)
 static int
 object_issubclass(PyThreadState *tstate, PyObject *derived, PyObject *cls)
 {
-    PyObject *checker;
-
     /* We know what type's __subclasscheck__ does. */
     if (PyType_CheckExact(cls)) {
         /* Quick test for an exact match */
@@ -2763,23 +2786,15 @@ object_issubclass(PyThreadState *tstate, PyObject *derived, PyObject *cls)
         return r;
     }
 
-    checker = _PyObject_LookupSpecial(cls, &_Py_ID(__subclasscheck__));
-    if (checker != NULL) {
-        int ok = -1;
-        if (_Py_EnterRecursiveCallTstate(tstate, " in __subclasscheck__")) {
-            Py_DECREF(checker);
-            return ok;
-        }
-        PyObject *res = PyObject_CallOneArg(checker, derived);
-        _Py_LeaveRecursiveCallTstate(tstate);
-        Py_DECREF(checker);
-        if (res != NULL) {
-            ok = PyObject_IsTrue(res);
-            Py_DECREF(res);
-        }
+    PyObject *res;
+    int found = call_special_method(tstate, cls, &_Py_ID(__subclasscheck__),
+                                    " in __subclasscheck__", derived, &res);
+    if (found > 0) {
+        int ok = PyObject_IsTrue(res);
+        Py_DECREF(res);
         return ok;
     }
-    else if (_PyErr_Occurred(tstate)) {
+    else if (found < 0) {
         return -1;
     }