What's the simplest way to subtract a month from a date in Python?

Question

If only timedelta had a month argument in it\'s constructor. So what\'s the simplest way to do this?

EDIT: I wasn\'t thinking too hard about this as was poin

Answer 1

Given a (year,month) tuple, where month goes from 1-12, try this:

>>> from datetime import datetime
>>> today = datetime.today()
>>> today
datetime.datetime(2010, 8, 6, 10, 15, 21, 310000)
>>> thismonth = today.year, today.month
>>> thismonth
(2010, 8)
>>> lastmonth = lambda (yr,mo): [(y,m+1) for y,m in (divmod((yr*12+mo-2), 12),)][0]
>>> lastmonth(thismonth)
(2010, 7)
>>> lastmonth( (2010,1) )
(2009, 12)

Assumes there are 12 months in every year.