#2503 make singletons compared with "is" not == or !=
Thanks to Wummel for the patch
diff --git a/Demo/classes/Dbm.py b/Demo/classes/Dbm.py
index 482806a..892c103 100755
--- a/Demo/classes/Dbm.py
+++ b/Demo/classes/Dbm.py
@@ -50,7 +50,7 @@
                 value = d[key]
                 print 'currently:', value
             value = input('value: ')
-            if value == None:
+            if value is None:
                 del d[key]
             else:
                 d[key] = value