The code appears to be correct, but I think we need to add an explicit import for ndbm in the __init__ file.  Right now I think it is only passing the tests because the test infrastructure imports all the dbm modules, including ndbm.

(I did not realize that doing 'import X.abc' causes 'abc' to be defined in the X.__init__.py module's namespace, but of course it must once I thought about it.)

The tricky bit here is writing a test case :)