Ask HN: best constraint solvers?

Do HNer's know of any good libraries for solving constraint problems? Specifically, I'm looking for a Python library, as the project I'm working on is a Python/Django app. I've done a little research into this and so far I've come up with:

http://labix.org/python-constraint

http://pypi.python.org/pypi/constraint/

Just wanted to see if there were better libraries out there I may have missed, or if I would be better off looking in different directions.