Update uses of string exceptions
diff --git a/Demo/rpc/rpc.py b/Demo/rpc/rpc.py
index 0a14bf2..08ef2fb 100644
--- a/Demo/rpc/rpc.py
+++ b/Demo/rpc/rpc.py
@@ -80,9 +80,9 @@
 
 
 # Exceptions
-BadRPCFormat = 'rpc.BadRPCFormat'
-BadRPCVersion = 'rpc.BadRPCVersion'
-GarbageArgs = 'rpc.GarbageArgs'
+class BadRPCFormat(Exception): pass
+class BadRPCVersion(Exception): pass
+class GarbageArgs(Exception): pass
 
 class Unpacker(xdr.Unpacker):