The ones that don't know Python going into it are typically locals. I had lunch with two Atlanta residents last year that were big C# guys but their job wanted them to learn Python. They sent them to a few tutorials and picked out a few talks that they wanted them to learn about, then the rest was up to them.

This number is lower, but I've talked to a few newbies that travel to PyCon as an educational tool paid for by their company. They've usually done a tutorial or two on the web, but they'll load up on the in-person tutorials and then hit whatever relevant talks they can find.

Companies send their employees to the training sessions, and since they're already there, they sometimes have them attend the conference too.

It's less that they don't "know" python - but rather that they only know a little. I know when I attended my first pycon, while I had been using Python a bunch I could have stood to spend some quality time in Zed's class, and generally sucking more knowledge out of things via the offer Zed is extending.

Also, more and more we are seeing people new to Python come in the Django door (as well as other frameworks) - these people may be comfortable with Django as a RAD framework, but don't quite yet consider themselves "python programmers" and so courses like this can help them.