https://github.com/python/cpython/commit/d4f52c445b9ef745bb1d1023be225f99b986e083
commit: d4f52c445b9ef745bb1d1023be225f99b986e083
branch: main
author: Kumar Aditya <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2026-09-22T11:16:30+05:30
summary:
gh-157526: Call `__instancecheck__` and `__subclasscheck__` without creating a
bound method (#157670)
files:
M Include/internal/pycore_object.h
M Modules/_testinternalcapi/test_cases.c.h
M Objects/abstract.c
M Objects/typeobject.c
M Python/bytecodes.c
M Python/executor_cases.c.h
M Python/generated_cases.c.h
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index 41786cb267c2e96..3ecc5e9f0554b09 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -957,7 +957,8 @@ extern int _PyObject_IsInstanceDictEmpty(PyObject *);
// Export for 'math' shared extension
PyAPI_FUNC(PyObject*) _PyObject_LookupSpecial(PyObject *, PyObject *);
-PyAPI_FUNC(int) _PyObject_LookupSpecialMethod(PyObject *attr, _PyStackRef
*method_and_self);
+PyAPI_FUNC(int) _PyObject_LookupSpecialMethod(PyObject *attr, _PyStackRef
*method,
+ _PyStackRef *self);
// Calls the method named `attr` on `self`, but does not set an exception if
// the attribute does not exist.
diff --git a/Modules/_testinternalcapi/test_cases.c.h
b/Modules/_testinternalcapi/test_cases.c.h
index 7a75e80298fcd82..a04770bd83b176e 100644
--- a/Modules/_testinternalcapi/test_cases.c.h
+++ b/Modules/_testinternalcapi/test_cases.c.h
@@ -10357,7 +10357,8 @@
ASSERT_WITHIN_STACK_BOUNDS(__FILE__, __LINE__);
_PyFrame_SetStackPointer(frame, stack_pointer);
_PyFrame_StackPointerValidate(frame);
- int err = _PyObject_LookupSpecialMethod(name, method_and_self);
+ int err = _PyObject_LookupSpecialMethod(name,
&method_and_self[0],
+ &method_and_self[1]);
_PyFrame_StackPointerInvalidate(frame);
if (err <= 0) {
if (err == 0) {
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 28f751965f36b94..da2a0b0c285b52b 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 +2636,37 @@ 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 self = PyStackRef_FromPyObjectBorrow(cls);
+ int found = _PyObject_LookupSpecialMethod(name, &cref.ref, &self);
+ if (found > 0) {
+ *res = NULL;
+ if (!_Py_EnterRecursiveCallTstate(tstate, where)) {
+ PyObject *method = PyStackRef_AsPyObjectBorrow(cref.ref);
+ PyObject *args[2] = {PyStackRef_AsPyObjectBorrow(self), 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(self);
+ _PyThreadState_PopCStackRef(tstate, &cref);
+ return found;
+}
+
static int
object_recursive_isinstance(PyThreadState *tstate, PyObject *inst, PyObject
*cls)
{
@@ -2672,26 +2704,16 @@ 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 +2753,6 @@ 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 +2783,15 @@ 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;
}
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 30958310227af0e..b9e114260424072 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -2931,17 +2931,22 @@ _PyObject_LookupSpecial(PyObject *self, PyObject *attr)
return res;
}
-// Lookup the method name `attr` on `self`. On entry, `method_and_self[0]`
-// is null and `method_and_self[1]` is `self`. On exit, `method_and_self[0]`
-// is the method object and `method_and_self[1]` is `self` if the method is
-// not bound.
+// Lookup the method name `attr` on `*self`. On entry, `*method` is null.
+// On exit, `*method` is the method object and `*self` is cleared if the
+// method is bound.
// Return 1 on success, -1 on error, and 0 if the method is missing.
+//
+// `method` must point to a location that the garbage collector can see,
+// such as the `ref` field of a `_PyCStackRef` or a slot on the interpreter
+// stack. A descriptor may be invoked while `*method` holds the only
+// reference to the method object, and that can trigger a collection.
int
-_PyObject_LookupSpecialMethod(PyObject *attr, _PyStackRef *method_and_self)
+_PyObject_LookupSpecialMethod(PyObject *attr, _PyStackRef *method,
+ _PyStackRef *self)
{
- PyObject *self = PyStackRef_AsPyObjectBorrow(method_and_self[1]);
- _PyType_LookupStackRefAndVersion(Py_TYPE(self), attr, &method_and_self[0]);
- PyObject *method_o = PyStackRef_AsPyObjectBorrow(method_and_self[0]);
+ PyObject *self_o = PyStackRef_AsPyObjectBorrow(*self);
+ _PyType_LookupStackRefAndVersion(Py_TYPE(self_o), attr, method);
+ PyObject *method_o = PyStackRef_AsPyObjectBorrow(*method);
if (method_o == NULL) {
return 0;
}
@@ -2953,14 +2958,14 @@ _PyObject_LookupSpecialMethod(PyObject *attr,
_PyStackRef *method_and_self)
descrgetfunc f = Py_TYPE(method_o)->tp_descr_get;
if (f != NULL) {
- PyObject *func = f(method_o, self, (PyObject *)(Py_TYPE(self)));
+ PyObject *func = f(method_o, self_o, (PyObject *)(Py_TYPE(self_o)));
if (func == NULL) {
return -1;
}
- PyStackRef_CLEAR(method_and_self[0]); // clear method
- method_and_self[0] = PyStackRef_FromPyObjectSteal(func);
+ PyStackRef_CLEAR(*method); // clear method
+ *method = PyStackRef_FromPyObjectSteal(func);
}
- PyStackRef_CLEAR(method_and_self[1]); // clear self
+ PyStackRef_CLEAR(*self); // clear self
return 1;
}
diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index fb0cdf4d65e060d..fdfd5a0e6090464 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -4141,7 +4141,8 @@ dummy_func(
op(_LOAD_SPECIAL, (method_and_self[2] -- method_and_self[2])) {
PyObject *name = _Py_SpecialMethods[oparg].name;
- int err = _PyObject_LookupSpecialMethod(name, method_and_self);
+ int err = _PyObject_LookupSpecialMethod(name, &method_and_self[0],
+ &method_and_self[1]);
if (err <= 0) {
if (err == 0) {
PyObject *owner =
PyStackRef_AsPyObjectBorrow(method_and_self[1]);
diff --git a/Python/executor_cases.c.h b/Python/executor_cases.c.h
index 9aad9e003765cf8..e3dc2e781a3bebd 100644
--- a/Python/executor_cases.c.h
+++ b/Python/executor_cases.c.h
@@ -16224,7 +16224,8 @@
PyObject *name = _Py_SpecialMethods[oparg].name;
_PyFrame_SetStackPointer(frame, stack_pointer);
_PyFrame_StackPointerValidate(frame);
- int err = _PyObject_LookupSpecialMethod(name, method_and_self);
+ int err = _PyObject_LookupSpecialMethod(name, &method_and_self[0],
+ &method_and_self[1]);
_PyFrame_StackPointerInvalidate(frame);
if (err <= 0) {
if (err == 0) {
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index 77c18b3d61fefc7..48f76ccf59f8bc8 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -10355,7 +10355,8 @@
ASSERT_WITHIN_STACK_BOUNDS(__FILE__, __LINE__);
_PyFrame_SetStackPointer(frame, stack_pointer);
_PyFrame_StackPointerValidate(frame);
- int err = _PyObject_LookupSpecialMethod(name, method_and_self);
+ int err = _PyObject_LookupSpecialMethod(name,
&method_and_self[0],
+ &method_and_self[1]);
_PyFrame_StackPointerInvalidate(frame);
if (err <= 0) {
if (err == 0) {
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