date_stuff.py

import datetime

DAYS_IN_MONTH = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]


def is_leap_year(year: int) -> int:
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)


def add_months(date: datetime.date, months: int) -> datetime.date:

    for _ in range(1, months + 1):

        year, month = date.year, date.month
        n_days = DAYS_IN_MONTH[month % 12] # the *next* month's days

        if is_leap_year(year) and date.month == 2: # febrero
            n_days += 1 # 28 --> 29

        date += datetime.timedelta(days=n_days)

    return date


if __name__ == "__main__":
    print(add_months(datetime.date(2022, 12, 30), 3))