FreezeGun is a library that allows your python tests to travel through time by mocking the datetime module.
Usage
Once the decorator or context manager have been invoked, all calls to datetime.datetime.now(), datetime.datetime.utcnow(), and datetime.date.today() will return the time that has been frozen.
via stevepulec.com
Hmmm, cool for writing tests for Pydap. I will definitely use this.