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In the old bsddb module a bsddb.btopen(..) database
would return the next available key+value on a
set_location(key) call when key did not exist in the
database. In python 2.3 (pybsddb) it raises an
exception and leaves the cursor at an unknown position
in the database.
[reported by Anthony McDonaly on comp.lang.python]
>>> import os
>>> import bsddb
>>> os.chdir('/tmp')
>>> my_data = bsddb.btopen('testing', 'c')
>>> for i in range(10):
... if i == 5:
... pass
... else:
... my_data['%d'%i] = '%d'%(i*i)
...
>>> my_data.keys()
['0', '1', '2', '3', '4', '6', '7', '8', '9']
>>> my_data.sync()
>>> my_data.set_location('5')
Traceback (most recent call last):
 File "<stdin>", line 1, in ?
 File
"/space/python-2.3/lib/python2.3/bsddb/__init__.py",
line 117, in set_location
 return self.dbc.set(key)
_bsddb.DBNotFoundError: (-30991, 'DB_NOTFOUND: No
matching key/data pair found')
Correct behaviour would have been to return ('6', '36')

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Yes this is a bug. The set_location() method should have been calling set_range() rather than set() internally.
Fixing that exposed another bug: set_range() would crash when looking up a key that exists in hash or rn databases.
Both bugs have been fixed to fix this one in python 2.4 & pybsddb CVS.
This bugfix should go into python 2.3.4.

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committed fix to head and release23-maint along with an associated fix for set_range where it could free() memory that it doesn't own on non B-Tree databases.