Fix Python – Return datetime object of previous month

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 pointed out below. Really what I wanted was any day in the last month because eventually I’m going to grab the year and month only. So given a datetime object, what’s the simplest way to return any datetime object that falls in the previous month?

Now we will see solution for issue: Return datetime object of previous month

Try this:

``````def monthdelta(date, delta):
m, y = (date.month+delta) % 12, date.year + ((date.month)+delta-1) // 12
if not m: m = 12
d = min(date.day, [31,
29 if y%4==0 and (not y%100==0 or y%400 == 0) else 28,
31,30,31,30,31,31,30,31,30,31][m-1])
return date.replace(day=d,month=m, year=y)

>>> for m in range(-12, 12):
print(monthdelta(datetime.now(), m))

2009-08-06 16:12:27.823000
2009-09-06 16:12:27.855000
2009-10-06 16:12:27.870000
2009-11-06 16:12:27.870000
2009-12-06 16:12:27.870000
2010-01-06 16:12:27.870000
2010-02-06 16:12:27.870000
2010-03-06 16:12:27.886000
2010-04-06 16:12:27.886000
2010-05-06 16:12:27.886000
2010-06-06 16:12:27.886000
2010-07-06 16:12:27.886000
2010-08-06 16:12:27.901000
2010-09-06 16:12:27.901000
2010-10-06 16:12:27.901000
2010-11-06 16:12:27.901000
2010-12-06 16:12:27.901000
2011-01-06 16:12:27.917000
2011-02-06 16:12:27.917000
2011-03-06 16:12:27.917000
2011-04-06 16:12:27.917000
2011-05-06 16:12:27.917000
2011-06-06 16:12:27.933000
2011-07-06 16:12:27.933000
>>> monthdelta(datetime(2010,3,30), -1)
datetime.datetime(2010, 2, 28, 0, 0)
>>> monthdelta(datetime(2008,3,30), -1)
datetime.datetime(2008, 2, 29, 0, 0)
``````

Edit Corrected to handle the day as well.

Edit See also the answer from puzzlement which points out a simpler calculation for `d`:

``````d = min(date.day, calendar.monthrange(y, m)[1])
``````

This question is answered By – Duncan