PyDbLite (small footprint untyped database engine in python)

PyDbLite is a pure-Python in-memory database engine, using Python list 
comprehensions as query language instead of SQL, which stores data in a 
cPickled file.

You can also use PyDbLite with MySQL and SQLite, as backends.  In order to 
use MySQL's adapter you will need MySQL-python (available on SlackBuilds.org).