advent.py

from datetime import datetime, timedelta

# utility functions for advent sundays

# calculate a given advent sunday (1-4), optionally for a given year
def advent(**kwargs) -> datetime:
    no = min(max(int(kwargs.get('advent', 1)), 1), 4)
    year = kwargs.get('year', datetime.now().year)
    xmas = datetime(year, 12, 25)
    advent_4 = xmas - timedelta(days=xmas.isoweekday())
    return advent_4 - timedelta(days=(7*(4-no)))

# calculate todays adventual status, returns a tuple with advent-number and daydiff to that sunday (0 == it is today)
def is_advent(a_day = None):
    if not a_day:
        a_day = now()
    a1_delta = 7+(datetime(a_day.year, a_day.month, a_day.day) - advent(advent=1)).days
    return a1_delta // 7, a1_delta % 7