You want the datetime module.
>>> from datetime import datetime, timedelta
>>> datetime(2008,08,18) - datetime(2008,09,26)
datetime.timedelta(4)
Another example:
>>> import datetime
>>> today = datetime.date.today()
>>> print(today)
2008-09-01
>>> last_year = datetime.date(2007, 9, 1)
>>> print(today - last_year)
366 days, 0:00:00
As pointed out here