properly lookup __instancecheck__ and __subclasscheck__

2 files changed, 29 insertions, 30 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 4da7e00..5fb7bfc 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2926,14 +2926,19 @@ PyObject_IsInstance(PyObject *inst, PyObject *cls)
 		Py_LeaveRecursiveCall();
 		return r;
 	}
-	if (name == NULL) {
-		name = PyString_InternFromString("__instancecheck__");
-		if (name == NULL)
-			return -1;
+
+	if (PyInstance_Check(cls)) {
+		checker = PyObject_GetAttrString(cls, "__instancecheck__");
+		if (checker == NULL) {
+			if (PyErr_ExceptionMatches(PyExc_AttributeError))
+				PyErr_Clear();
+			else
+				return -1;
+		}
+	}
+	else {
+		checker = _PyObject_LookupSpecial(cls, "__instancecheck__", &name);
 	}
-	checker = PyObject_GetAttr(cls, name);
-	if (checker == NULL && PyErr_Occurred())
-		PyErr_Clear();
 	if (checker != NULL) {
 		PyObject *res;
 		int ok = -1;
@@ -3008,14 +3013,21 @@ PyObject_IsSubclass(PyObject *derived, PyObject *cls)
  		Py_LeaveRecursiveCall();
  		return r;
  	}
-	if (name == NULL) {
-		name = PyString_InternFromString("__subclasscheck__");
-		if (name == NULL)
+	if (PyInstance_Check(cls)) {
+		PyErr_Fetch(&t, &v, &tb);
+		checker = PyObject_GetAttr(cls, name);
+		if (checker == NULL &&
+		    !PyErr_ExceptionMatches(PyExc_AttributeError)) {
+			Py_XDECREF(t);
+			Py_XDECREF(v);
+			Py_XDECREF(tb);
 			return -1;
+		}
+		PyErr_Restore(t, v, tb);
+	}
+	else {
+		checker = _PyObject_LookupSpecial(cls, "__subclasscheck__", &name);
 	}
-	PyErr_Fetch(&t, &v, &tb);
-	checker = PyObject_GetAttr(cls, name);
-	PyErr_Restore(t, v, tb);
 	if (checker != NULL) {
 		PyObject *res;
 		int ok = -1;
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index fabdd9d..8c49096 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -586,14 +586,6 @@ type___instancecheck__(PyObject *type, PyObject *inst)
 
 
 static PyObject *
-type_get_instancecheck(PyObject *type, void *context)
-{
-	static PyMethodDef ml = {"__instancecheck__",
-				 type___instancecheck__, METH_O };
-	return PyCFunction_New(&ml, type);
-}
-
-static PyObject *
 type___subclasscheck__(PyObject *type, PyObject *inst)
 {
 	switch (_PyObject_RealIsSubclass(inst, type)) {
@@ -606,13 +598,6 @@ type___subclasscheck__(PyObject *type, PyObject *inst)
 	}
 }
 
-static PyObject *
-type_get_subclasscheck(PyObject *type, void *context)
-{
-	static PyMethodDef ml = {"__subclasscheck__",
-				 type___subclasscheck__, METH_O };
-	return PyCFunction_New(&ml, type);
-}
 
 static PyGetSetDef type_getsets[] = {
 	{"__name__", (getter)type_name, (setter)type_set_name, NULL},
@@ -622,8 +607,6 @@ static PyGetSetDef type_getsets[] = {
 	 (setter)type_set_abstractmethods, NULL},
 	{"__dict__",  (getter)type_dict,  NULL, NULL},
 	{"__doc__", (getter)type_get_doc, NULL, NULL},
-	{"__instancecheck__", (getter)type_get_instancecheck, NULL, NULL},
-	{"__subclasscheck__", (getter)type_get_subclasscheck, NULL, NULL},
 	{0}
 };
 
@@ -2674,6 +2657,10 @@ static PyMethodDef type_methods[] = {
 	 PyDoc_STR("mro() -> list\nreturn a type's method resolution order")},
 	{"__subclasses__", (PyCFunction)type_subclasses, METH_NOARGS,
 	 PyDoc_STR("__subclasses__() -> list of immediate subclasses")},
+	{"__instancecheck__", type___instancecheck__, METH_O,
+	 PyDoc_STR("__instancecheck__() -> check if an object is an instance")},
+	{"__subclasscheck__", type___subclasscheck__, METH_O,
+	 PyDoc_STR("__subclasschck__ -> check if an class is a subclass")},
 	{0}
 };