monthdelta.py

from datetime import datetime, date
import calendar

def monthdelta(dt0, months=1):
    year = dt0.year + (dt0.month + months) // 12
    month = 1 + (dt0.month + months - 1) % 12
    maxday = calendar.monthrange(year, month)[1]
    if maxday < dt0.day:
        d = date(year, month, maxday)
    else:
        d = date(year, month, dt0.day)
    return datetime.combine(date=d, time=dt0.time())