SF bug 542984.

Change type_get_doc (the get function for __doc__) to look in tp_dict
more often, and if it finds a descriptor in tp_dict, to call it (with
a NULL instance).  This means you can add a __doc__ descriptor to a
new-style class that returns instance docs when called on an instance,
and class docs when called on a class -- or the same docs in either
case, but lazily computed.

I'll also check this into the 2.2 maintenance branch.

1 files changed, 11 insertions, 7 deletions

diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index deb7320..f647d57 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -82,15 +82,19 @@ static PyObject *
 type_get_doc(PyTypeObject *type, void *context)
 {
 	PyObject *result;
-	if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
-		if (type->tp_doc == NULL) {
-			Py_INCREF(Py_None);
-			return Py_None;
-		}
+	if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE) && type->tp_doc != NULL)
 		return PyString_FromString(type->tp_doc);
-	}
 	result = PyDict_GetItemString(type->tp_dict, "__doc__");
-	Py_INCREF(result);
+	if (result == NULL) {
+		result = Py_None;
+		Py_INCREF(result);
+	}
+	else if (result->ob_type->tp_descr_get) {
+		result = result->ob_type->tp_descr_get(result, NULL, type);
+	}
+	else {
+		Py_INCREF(result);
+	}
 	return result;
 }