Python: add days to date without any modules

Question

I wonder is there any simple and elegant way to add days to date in python without using any modules.
Imaging we have code like this:

from datetime import date, timedelta
date1 = date(2008, 1, 10)
date2 = date1 + timedelta(days=555)

How we can do this in pure python? Even skipping the even years checks