bsddb 4.1.6:

* Extended DB & DBEnv set_get_returns_none functionality to take a
   "level" instead of a boolean flag.  The boolean 0 and 1 values still
   have the same effect.  A value of 2 extends the "return None instead
   of raising an exception" behaviour to the DBCursor set methods.
   This will become the default behaviour in pybsddb 4.2.
 * Fixed a typo in DBCursor.join_item method that made it crash instead
   of returning a value.  Obviously nobody uses it.  Wrote a test case
   for join and join_item.

Lib/bsddb/dbtables.py

@@ -155,6 +155,9 @@ class bsdTableDB :
         if truncate:
             myflags |= DB_TRUNCATE
         self.db = DB(self.env)
+        # this code relies on DBCursor.set* methods to raise exceptions
+        # rather than returning None
+        self.db.set_get_returns_none(1)
         # allow duplicate entries [warning: be careful w/ metadata]
         self.db.set_flags(DB_DUP)
         self.db.open(filename, DB_BTREE, dbflags | myflags, mode)