delta_months.py

def delta_months(date, months):
    sign = months / abs(months)
    current_day = date.day
    date -= timedelta(current_day)
    while months:
        month_days = calendar.monthrange(date.year, date.month)[1]
        date += timedelta(month_days * sign)
        months += sign * -1
    if current_day > month_days:
        current_day = month_days
    return date + timedelta(days=current_day)

def delta_months2(date, months):
    sign = months / abs(months)
    year, month = divmod(months, 12)
    m = [x % 13 for x in range(12, 25) if x % 13]
    newmonth = m[(date.month + month) % 12]
    newyear = date.year + year * sign
    newday = date.day
    month_days = calendar.monthrange(newyear, newmonth)[1]
    if date.day > month_days:
        newday = month_days
    return date.replace(year=newyear, month=newmonth, day=newday)