properly lookup __instancecheck__ and __subclasscheck__

Lib/test/test_descr.py

@@ -1683,16 +1683,25 @@ order (MRO) for bases """
             return 0
         def stop(self):
             raise StopIteration
+        def return_true(self, thing=None):
+            return True
+        def do_isinstance(obj):
+            return isinstance(int, obj)
+        def do_issubclass(obj):
+            return issubclass(int, obj)
 
         # It would be nice to have every special method tested here, but I'm
         # only listing the ones I can remember outside of typeobject.c, since it
         # does it right.
         specials = [
-            ("__unicode__", unicode, hello, {}),
+            ("__unicode__", unicode, hello, set(), {}),
-            ("__reversed__", reversed, empty_seq, {}),
+            ("__reversed__", reversed, empty_seq, set(), {}),
-            ("__length_hint__", list, zero,
+            ("__length_hint__", list, zero, set(),
              {"__iter__" : iden, "next" : stop}),
-            ("__sizeof__", sys.getsizeof, zero, {}),
+            ("__sizeof__", sys.getsizeof, zero, set(), {}),
+            ("__instancecheck__", do_isinstance, return_true, set(), {}),
+            ("__subclasscheck__", do_issubclass, return_true,
+             set(("__bases__",)), {}),
             # These two fail because the compiler generates LOAD_ATTR to look
             # them up.  We'd have to add a new opcode to fix this, and it's
             # probably not worth it.
@@ -1704,7 +1713,9 @@ order (MRO) for bases """
             def __getattr__(self, attr, test=self):
                 test.fail("__getattr__ called with {0}".format(attr))
             def __getattribute__(self, attr, test=self):
-                test.fail("__getattribute__ called with {0}".format(attr))
+                if attr not in ok:
+                    test.fail("__getattribute__ called with {0}".format(attr))
+                return object.__getattribute__(attr)
         class SpecialDescr(object):
             def __init__(self, impl):
                 self.impl = impl
@@ -1713,7 +1724,7 @@ order (MRO) for bases """
                 return self.impl.__get__(obj, owner)
 
 
-        for name, runner, meth_impl, env in specials:
+        for name, runner, meth_impl, ok, env in specials:
             class X(Checker):
                 pass
             for attr, obj in env.iteritems():

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 (PyInstance_Check(cls)) {
-		if (name == NULL)
+		checker = PyObject_GetAttrString(cls, "__instancecheck__");
-			return -1;
+		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) {
+	if (PyInstance_Check(cls)) {
-		name = PyString_InternFromString("__subclasscheck__");
+		PyErr_Fetch(&t, &v, &tb);
-		if (name == NULL)
+		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;

Objects/typeobject.c

@@ -585,14 +585,6 @@ 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)
 {
@@ -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}
 };