Only the CLI utility in Play used Python, and the newest version has replaced this dependency with Scala/SBT instead. I imagine the original reason for using Python for the CLI was because it's pretty damn easy to do that in Python.
Python is great for that sort of thing - but there do exist CLI helper libraries for Java in Apache Commons that make it almost as nice. It's just wierd to me to make development tooling for a langage in a different language - and indeed, if you find yourself doing this you might want to ask yourself why. (Of course there's a clear market reason - the hosted Ruby on Rails market is locked up by Heroku, but the hosted Java market, apart from a subset of JEE supported by GAE, doesn't even exist.)
