The General Multiprecision PYthon project, aka GMPY, (http://gmpy.sourceforge.net/) focuses on Python-usable modules providing multiprecision arithmetic functionality to Python programmers. It aims to include integral, rational, and floating-point arithmetic in any base. At the moment (March 2007) it wraps and exposes to Python (a lot of) the functionality of the GNU Multiple Precision library, GMP (http://gmplib.org/).
GMPY is a free software project released under the LGPL license.