The following are links to scientific software libraries that have been recommended by Python users.
[http://www.fftw.org FFTW] claims to be the Fastest Fourier Transform in the West.
The [http://starship.python.net/crew/hinsen/MMTK/ MMTK] Molecular Modeling Toolkit, by Konrad Hinsen, is a set of modules for molecular simulation applications.
[http://www.amk.ca/python/code/crypto.html Python Cryptography Modules] An extensive toolkit including Python extensions for encryption, authentication, key exchange, and other cryptography operations.