apply_calendar_month_delta.py

import datetime

def apply_calendar_month_delta(datetime_in, month_delta):
	"""
	Applies an (integer) @month_delta to @datetime_in. Cheats on days, clamping them to (0,28] to avoid complexities.
	
	>>> from datetime import date
	>>> apply_calendar_month_delta(date(2014, 1, 3), -1)
	datetime.date(2013, 12, 3)
	>>> apply_calendar_month_delta(date(2014, 9, 3), 6)
	datetime.date(2015, 3, 3)
	>>> apply_calendar_month_delta(date(2011, 10, 31), 5)
	datetime.date(2012, 3, 28)
	>>> apply_calendar_month_delta(date(2012, 3, 25), -15)
	datetime.date(2010, 12, 25)
	"""
	return datetime.date(year=datetime_in.year + (((datetime_in.month-1)+month_delta) // 12), month=(((datetime_in.month-1)+month_delta)%12)+1 , day=min(datetime_in.day, 28))