Index: Objects/abstract.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/abstract.c,v
retrieving revision 2.119
diff -u -r2.119 abstract.c
--- Objects/abstract.c	1 Mar 2003 01:44:32 -0000	2.119
+++ Objects/abstract.c	20 Mar 2004 16:02:11 -0000
@@ -2035,8 +2035,8 @@
 	return -1;
 }
 
-int
-PyObject_IsInstance(PyObject *inst, PyObject *cls)
+static int
+recursive_IsInstance(PyObject *inst, PyObject *cls, int recursion_depth)
 {
 	PyObject *icls;
 	static PyObject *__class__ = NULL;
@@ -2071,14 +2071,19 @@
 		}
 	}
 	else if (PyTuple_Check(cls)) {
-		/* Not a general sequence -- that opens up the road to
-		   recursion and stack overflow. */
 		int i, n;
 
+                if (!recursion_depth) {
+                    PyErr_SetString(PyExc_RuntimeError,
+                                    "Recursion depth exceeded");
+                    return NULL;
+                }
+
 		n = PyTuple_GET_SIZE(cls);
 		for (i = 0; i < n; i++) {
-			retval = PyObject_IsInstance(
-				inst, PyTuple_GET_ITEM(cls, i));
+			retval = recursive_IsInstance(
+				inst, PyTuple_GET_ITEM(cls, i),
+                                recursion_depth-1);
 			if (retval != 0)
 				break;
 		}
@@ -2103,7 +2108,13 @@
 }
 
 int
-PyObject_IsSubclass(PyObject *derived, PyObject *cls)
+PyObject_IsInstance(PyObject *inst, PyObject *cls)
+{
+    return recursive_IsInstance(inst, cls, Py_GetRecursionLimit());
+}
+
+static int
+recursive_IsSubclass(PyObject *derived, PyObject *cls, int recursion_depth)
 {
 	int retval;
 
@@ -2115,9 +2126,17 @@
 		if (PyTuple_Check(cls)) {
 			int i;
 			int n = PyTuple_GET_SIZE(cls);
+
+                        if (!recursion_depth) {
+                            PyErr_SetString(PyExc_RuntimeError,
+                                            "Recursion depth exceeded");
+                            return NULL;
+                        }
+                        
 			for (i = 0; i < n; ++i) {
-				retval = PyObject_IsSubclass(
-					derived, PyTuple_GET_ITEM(cls, i));
+				retval = recursive_IsSubclass(
+					derived, PyTuple_GET_ITEM(cls, i),
+                                        recursion_depth-1);
 				if (retval != 0) {
 					/* either found it, or got an error */
 					return retval;
@@ -2143,6 +2162,12 @@
 	return retval;
 }
 
+int
+PyObject_IsSubclass(PyObject *derived, PyObject *cls)
+{
+    return recursive_IsSubclass(derived, cls, Py_GetRecursionLimit());
+}
+
 PyObject *
 PyObject_GetIter(PyObject *o)
 {