Can anyone suggest any good payment processing libraries for python/django?
Perhaps you can find some usefull code hints/modules looking at Satchmo: Satchmo Homepage
The most developed Django solution is Satchmo with support for Authorize.Net, TrustCommerce, CyberSource, PayPal, Google Checkout, and Protx.
The new kid on the Django block is django-lfs which looks like only support for PayPal at the moment, and even that may not be complete.
For general Python the main player is getpaid
Django paypal is very cool. I've used in on couple of my projects. It is relatively easy to integrate with an existing website. Satchmo is good, if you want a full internet store, but if you want to sell just couple items from your website, which is devoted to something else, you will find Satchmo to be very heavy (a lot of dependencies to install, really complicates your admin).
There is Django payments application called Mamona which currently supports only PayPal. It can be used with any existing application without changing it's code. Basically, it can use any exiting model as order.