"b" as in bug, or "b" as in behavior? Having only recently learned that both exist I now am never sure what is meant by BDD.
It's safe to assume behaviour driven development when you see BDD. Bug driven development is just a term used to point out a project has little or no test suite and that the devs don't seem to care about testing.
In Python? I'd recommend behave. You can mix it with selenium if you're looking for some web coverage as well.