Compute easter/ascension/pentecost dates

compute_specific_closed_days.py

from datetime import date
from datetime import timedelta

def calc_easter_sunday(year: int) -> date:
    """
    Returns Easter as a date object.
    An implementation of Butcher's Algorithm for determining the date of Easter for the Western church.
    Works for any date in the Gregorian calendar (1583 and onward).
    Reference: http://code.activestate.com/recipes/576517-calculate-easter-western-given-a-year/
    """
    a = year % 19
    b = year // 100
    c = year % 100
    d = (19 * a + b - b // 4 - ((b - (b + 8) // 25 + 1) // 3) + 15) % 30
    e = (32 + 2 * (b % 4) + 2 * (c // 4) - d - (c % 4)) % 7
    f = d + e - 7 * ((a + 11 * d + 22 * e) // 451) + 114
    month = f // 31
    day = f % 31 + 1    
    return date(year, month, day)

def calc_easter_monday(year: int) -> date:
    "Returns Easter Monday as a date object."
    return calc_easter_sunday(year)+timedelta(days=1)
def calc_ascension_thursday(year: int) -> date:
    "Returns Ascension day as a date object."
    return calc_easter_sunday(year)+timedelta(days=39)
def calc_pentecost_sunday(year: int) -> date:
    "Returns Pentecost Sunday as a date object."
    return calc_easter_sunday(year)+timedelta(days=49)
def calc_pentecost_monday(year: int) -> date:
    "Returns Pentecost Monday as a date object."
    return calc_easter_sunday(year)+timedelta(days=50)