SF bug #475327: type() produces incorrect error msg

object.h:  Added PyType_CheckExact macro.

typeobject.c, type_new():

+ Use the new macro.
+ Assert that the arguments have the right types rather than do incomplete
  runtime checks "sometimes".
+ If this isn't the 1-argument flavor() of type, and there aren't 3 args
  total, produce a "types() takes 1 or 3 args" msg before
  PyArg_ParseTupleAndKeywords produces a "takes exactly 3" msg.

Include/object.h

@@ -312,6 +312,7 @@ extern DL_IMPORT(PyTypeObject) PyBaseObject_Type; /* built-in 'object' */
 extern DL_IMPORT(PyTypeObject) PySuper_Type; /* built-in 'super' */
 
 #define PyType_Check(op) PyObject_TypeCheck(op, &PyType_Type)
+#define PyType_CheckExact(op) ((op)->ob_type == &PyType_Type)
 
 extern DL_IMPORT(int) PyType_Ready(PyTypeObject *);
 extern DL_IMPORT(PyObject *) PyType_GenericAlloc(PyTypeObject *, int);

Objects/typeobject.c

@@ -713,13 +713,28 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
 	PyMemberDef *mp;
 	int i, nbases, nslots, slotoffset, add_dict, add_weak;
 
+	assert(args != NULL && PyTuple_Check(args));
+	assert(kwds == NULL || PyDict_Check(kwds));
+
 	/* Special case: type(x) should return x->ob_type */
-	if (metatype == &PyType_Type &&
-	    PyTuple_Check(args) && PyTuple_GET_SIZE(args) == 1 &&
-	    (kwds == NULL || (PyDict_Check(kwds) && PyDict_Size(kwds) == 0))) {
-		PyObject *x = PyTuple_GET_ITEM(args, 0);
-		Py_INCREF(x->ob_type);
-		return (PyObject *) x->ob_type;
+	{
+		const int nargs = PyTuple_GET_SIZE(args);
+		const int nkwds = kwds == NULL ? 0 : PyDict_Size(kwds);
+
+		if (PyType_CheckExact(metatype) && nargs == 1 && nkwds == 0) {
+			PyObject *x = PyTuple_GET_ITEM(args, 0);
+			Py_INCREF(x->ob_type);
+			return (PyObject *) x->ob_type;
+		}
+
+		/* SF bug 475327 -- if that didn't trigger, we need 3
+		   arguments. but PyArg_ParseTupleAndKeywords below may give
+		   a msg saying type() needs exactly 3. */
+		if (nargs + nkwds != 3) {
+			PyErr_SetString(PyExc_TypeError,
+					"type() takes 1 or 3 arguments");
+			return NULL;
+		}
 	}
 
 	/* Check arguments: (name, bases, dict) */