Increment and decrement month of date in python

incdecmonth.py

import datetime


def inc_month(dt, months):
    '''
    "months" can be positive or negative
    If day in new month can't be the same, it will be the the closest possible.
    '''
    newmonth = (((dt.month - 1) + months) % 12) + 1
    newyear = dt.year + (((dt.month - 1) + months) // 12)
    newday = dt.day
    newdt = None
    while newdt is None:
        try:
            newdt = datetime.date(newyear, newmonth, newday)
            return newdt
        except ValueError:
            newday -= 1


def dec_month(dt, months):
    return inc_month(dt, -months)