Backport Martin's checkin 1.6:

Fix bug #422702: Make flag argument to open optional, and document it that way.

Lib/dbhash.py

@@ -12,5 +12,5 @@ __all__ = ["error","open"]
 
 error = bsddb.error                     # Exported for anydbm
 
-def open(file, flag, mode=0666):
+def open(file, flag = 'r', mode=0666):
     return bsddb.hashopen(file, flag, mode)