gauss_easter.py

"""
https://en.wikipedia.org/wiki/Computus#Gauss'_Easter_algorithm
"""

importmath
fromdatetimeimportUTC, datetime, timedelta


defgauss_easter(year: int) ->datetime:
"""
 Calculation Gregorian easter date for given year

 >>> gauss_easter(2007)
 datetime.datetime(2007, 4, 8, 0, 0, tzinfo=datetime.timezone.utc)

 >>> gauss_easter(2008)
 datetime.datetime(2008, 3, 23, 0, 0, tzinfo=datetime.timezone.utc)

 >>> gauss_easter(2020)
 datetime.datetime(2020, 4, 12, 0, 0, tzinfo=datetime.timezone.utc)

 >>> gauss_easter(2021)
 datetime.datetime(2021, 4, 4, 0, 0, tzinfo=datetime.timezone.utc)
 """
metonic_cycle=year%19
julian_leap_year=year%4
non_leap_year=year%7
leap_day_inhibits=math.floor(year/100)
lunar_orbit_correction=math.floor((13+8*leap_day_inhibits) /25)
leap_day_reinstall_number=leap_day_inhibits/4
secular_moon_shift= (
15-lunar_orbit_correction+leap_day_inhibits-leap_day_reinstall_number
 ) %30
century_starting_point= (4+leap_day_inhibits-leap_day_reinstall_number) %7

# days to be added to March 21
days_to_add= (19*metonic_cycle+secular_moon_shift) %30

# PHM -> Paschal Full Moon
days_from_phm_to_sunday= (
2*julian_leap_year
+4*non_leap_year
+6*days_to_add
+century_starting_point
 ) %7

ifdays_to_add==29anddays_from_phm_to_sunday==6:
returndatetime(year, 4, 19, tzinfo=UTC)
elifdays_to_add==28anddays_from_phm_to_sunday==6:
returndatetime(year, 4, 18, tzinfo=UTC)
else:
returndatetime(year, 3, 22, tzinfo=UTC) +timedelta(
days=int(days_to_add+days_from_phm_to_sunday)
 )


if__name__=="__main__":
foryearin (1994, 2000, 2010, 2021, 2023, 2032, 2100):
tense="will be"ifyear>datetime.now(tz=UTC).yearelse"was"
print(f"Easter in {year}{tense}{gauss_easter(year)}")