diff --git a/Lib/xmlrpclib.py b/Lib/xmlrpclib.py
index 8c6f799..d1edf20 100644
--- a/Lib/xmlrpclib.py
+++ b/Lib/xmlrpclib.py
@@ -496,7 +496,7 @@
     def opencontainer(self, value):
         if value:
             i = id(value)
-            if self.memo.has_key(i):
+            if i in self.memo:
                 raise TypeError, "cannot marshal recursive data structures"
             self.memo[i] = None