>>> import datetime
>>> datetime.datetime.now() - datetime.timedelta(days=7)
datetime.datetime(2013, 12, 6, 10, 29, 37, 596779)
If you really just want the date, you can call the date method:
>>> (datetime.datetime.now() - datetime.timedelta(days=7)).date()
datetime.date(2013, 12, 6)
Or, work with dates to begin with as suggested by unutbu.