In my experience a lot of Python programmers move on to learning the functional Python features and libraries and then after they get that down, the eventually jump ship to a mainly-functional language (a lot of people seem to move to Haskell, I personally moved to Clojure).
This is based on my own personal experience, that of Python Ireland members and from things I've read or seen (here on HN and elsewhere).
Do you mind elaborating on what 'functional' libraries exist in python? I've practiced a bit using the whole map-reduce paradigm in different ways in python, but I'm not really sure what you mean beyond that.
I once read a quote that when you're using itertools frequently enough in your Python code you're one step away from jumping to a language like Haskell.
I've heard that the OReilly Haskell book was one of the most bought books at PyCon.
My progression went similarly - I started using map, reduce, filter and list comprehension a lot, then moved on to itertools and functools and then decided what I really wanted was a functional by default language. That, the great concurrency support and the desire to learn a lisp-based language properly[1] made me choose Clojure.
It seems that this progression is actually fairly common. I still use Python for quick'n'dirty scripts (especially as a shell scripting alternative) and for web development (for other people; I use Clojure for my own code).
[1] I already knew some Scheme, but never used it for any real projects.
This is based on my own personal experience, that of Python Ireland members and from things I've read or seen (here on HN and elsewhere).