There are several A/B split testing modules/plugins for Rails.
http://github.com/paulmars/seven_minute_abs
http://www.bingocardcreator.com/abingo
http://vanity.labnotes.org/
etc.
Is there anything similar for Python?
It's only at version 0.1.2 so far, but Swab looks promising. Example of testing two sizes of a form button:
from swab import Swab
s = Swab('/tmp/.swab-test-data')
s.addexperiment('button-size', ['default', 'larger'], 'order-completed')