1 files changed, 86 insertions, 8 deletions

diff --git a/Python/traceback.c b/Python/traceback.c
index 1c26ba2..b96ca47 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -12,8 +12,6 @@
 #define OFF(x) offsetof(PyTracebackObject, x)
 
 static PyMemberDef tb_memberlist[] = {
-	{"tb_next",	T_OBJECT,	OFF(tb_next), READONLY},
-	{"tb_frame",	T_OBJECT,	OFF(tb_frame), READONLY},
 	{"tb_lasti",	T_INT,		OFF(tb_lasti), READONLY},
 	{"tb_lineno",	T_INT,		OFF(tb_lineno), READONLY},
 	{NULL}	/* Sentinel */
@@ -45,6 +43,81 @@ tb_clear(PyTracebackObject *tb)
 	Py_CLEAR(tb->tb_frame);
 }
 
+static PyObject *
+tb_get_next(PyTracebackObject *tb) {
+	if (tb->tb_next) {
+		Py_INCREF(tb->tb_next);
+		return (PyObject *)tb->tb_next;
+	}
+	Py_RETURN_NONE;
+}
+
+static int
+tb_set_next(PyTracebackObject *tb, PyObject *new, void *context) {
+	if (!new) {
+		PyErr_SetString(PyExc_TypeError, "can't delete tb_next");
+		return -1;
+	}
+	else if (new == Py_None) {
+		new = NULL;
+	}
+	else if (PyTraceBack_Check(new)) {
+		/* Check for cycles in the traceback. */
+		PyTracebackObject *current = (PyTracebackObject *)new;
+		do {
+			if (tb == current) {
+				PyErr_SetString(PyExc_ValueError, "cycle in traceback");
+				return -1;
+			}
+		} while ((current = current->tb_next));
+		Py_INCREF(new);
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"tb_next must be an traceback object");
+		return -1;
+	}
+	Py_XDECREF(tb->tb_next);
+	tb->tb_next = (PyTracebackObject *)new;
+	return 0;
+}
+
+static PyObject *
+tb_get_frame(PyTracebackObject *tb) {
+	if (tb->tb_frame) {
+		Py_INCREF(tb->tb_frame);
+		return (PyObject *)tb->tb_frame;
+	}
+	Py_RETURN_NONE;
+}
+
+static int
+tb_set_frame(PyTracebackObject *tb, PyObject *new, void *context) {
+	if (!new) {
+		PyErr_SetString(PyExc_TypeError,
+				"can't delete tb_frame attribute");
+		return -1;
+	}
+	else if (new == Py_None) {
+		new = NULL;
+	}
+	else if (PyFrame_Check(new)) {
+		Py_INCREF(new);
+	}
+	else {
+		PyErr_SetString(PyExc_TypeError,
+				"tb_frame must be a frame object");
+		return -1;
+	}
+	tb->tb_frame = (PyFrameObject *)new;
+	return 0;
+}
+
+static PyGetSetDef tb_getset[] = {
+	{"tb_next", (getter)tb_get_next, (setter)tb_set_next, NULL},
+	{"tb_frame", (getter)tb_get_frame, (setter)tb_set_frame, NULL},
+};
+
 PyTypeObject PyTraceBack_Type = {
 	PyVarObject_HEAD_INIT(&PyType_Type, 0)
 	"traceback",
@@ -75,7 +148,7 @@ PyTypeObject PyTraceBack_Type = {
 	0,					/* tp_iternext */
 	0,					/* tp_methods */
 	tb_memberlist,			        /* tp_members */
-	0,			                /* tp_getset */
+	tb_getset,			        /* tp_getset */
 	0,					/* tp_base */
 	0,					/* tp_dict */
 };
@@ -245,11 +318,16 @@ tb_printinternal(PyTracebackObject *tb, PyObject *f, long limit)
 	}
 	while (tb != NULL && err == 0) {
 		if (depth <= limit) {
-			err = tb_displayline(f,
-			    PyString_AsString(
-				    tb->tb_frame->f_code->co_filename),
-			    tb->tb_lineno,
-			    PyString_AsString(tb->tb_frame->f_code->co_name));
+			PyFrameObject *frame = tb->tb_frame;
+			char *filename, *name;
+			if (frame) {
+				filename = PyString_AS_STRING(frame->f_code->co_filename);
+				name = PyString_AS_STRING(frame->f_code->co_name);
+			}
+			else {
+				filename = name = "unkown (no frame on traceback)";
+			}
+			err = tb_displayline(f, filename, tb->tb_lineno, name);
 		}
 		depth--;
 		tb = tb->tb_next;