Is SQLite suitable for use as a read only cache on a web server?
Ok after much research and performance testing, SQLite is suitable for this. It has good request concurrency on static data. SQLite only becomes an issue if you are doing writes as well as heavy reads.
More information here:
if usage case is just a cache why don't you use something like http://memcached.org/.
You can find memcached bindings for python in pypi repository.
Another options is that you use materialized views in postgres, this way you will keep things simple and have everything in one place.
http://tech.jonathangardner.net/wiki/PostgreSQL/Materialized_Views