methods to calculate datetime from days, months and years delta in python

periods_delta.py

import datetime

def days_period_to_datetime(dd):
    now = datetime.datetime.utcnow()
    return now + datetime.timedelta(days=dd)


def months_period_to_datetime(mm):
    now = datetime.datetime.utcnow()
    new_day = now.day

    month_sum = now.month + mm
    if month_sum <= 12:
        new_month = month_sum
    else:
        new_month = month_sum % 12

    new_year = int(now.year + month_sum / 12)
    try:
        return now.replace(year=new_year, month=new_month, day=new_day)
    except ValueError:
        # Must be a month whose days are less than 31
        if new_month == 2:
            try:
                return now.replace(year=new_year, month=new_month, day=29)
            except ValueError:  # Must be 28 days then
                return now.replace(year=new_year, month=new_month, day=28)

        if new_month in (4, 6, 9, 11):
            return now.replace(year=new_year, month=new_month, day=30)


def years_period_to_datetime(yy):
    now = datetime.datetime.utcnow()
    try:
        return now.replace(year=now.year + yy)
    except ValueError:
        # Must be 2/29 if it is an Exception!
        assert now.month == 2 and now.day == 29
        return now.replace(month=2, day=28, year=now.year + yy)


print days_period_to_datetime(44)
print days_period_to_datetime(0)

print months_period_to_datetime(5)
print months_period_to_datetime(18)

print years_period_to_datetime(1)
print years_period_to_datetime(17)