Move backwards and forwards in month long chunks of time

monthdelta.py

def monthdelta(date, delta):
    '''
    Acts like datetime.timedelta but deals with months

    `date`: A datetime object representing the base date
    `delta`: An integer representing the offset (-ve for going back in time)

    Found at : http://stackoverflow.com/a/3425124/364088

    '''
    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%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)