That said, we use python inside of PG, and it's awesome. It's not really any more powerful than PG/SQL(their built-in language) i.e. in terms of what you can do in the DB itself.
Our main app is also python, so we have a continuity of language from front-end to back-end. We do have some DB functions that take advantage of python's flexibilities, but like I said, we try to keep external modules and craziness out of the PG backend if possible. Sometimes there is no help for it, and you do what you must, and it's very handy that you can just go do it.
edit: i'm still trying to train myself to think in a relational way.