diff --git a/python/helpers/StdlibTypes3.properties b/python/helpers/StdlibTypes3.properties
index 26712128c7db..11c642c8d5b5 100644
--- a/python/helpers/StdlibTypes3.properties
+++ b/python/helpers/StdlibTypes3.properties
@@ -249,6 +249,9 @@ __builtin__.str.find = \
   :type end: int or long or None \n\
   :rtype: int or long \n\
 
+__builtin__.str.format = \
+  :rtype: str \n\
+
 __builtin__.str.index = \
   :type sub: str \n\
   :type start: int or long or None \n\