diff options
Diffstat (limited to 'venv/lib/python3.11/site-packages/dateutil/easter.py')
-rw-r--r-- | venv/lib/python3.11/site-packages/dateutil/easter.py | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/venv/lib/python3.11/site-packages/dateutil/easter.py b/venv/lib/python3.11/site-packages/dateutil/easter.py new file mode 100644 index 0000000..f74d1f7 --- /dev/null +++ b/venv/lib/python3.11/site-packages/dateutil/easter.py @@ -0,0 +1,89 @@ +# -*- coding: utf-8 -*- +""" +This module offers a generic Easter computing method for any given year, using +Western, Orthodox or Julian algorithms. +""" + +import datetime + +__all__ = ["easter", "EASTER_JULIAN", "EASTER_ORTHODOX", "EASTER_WESTERN"] + +EASTER_JULIAN = 1 +EASTER_ORTHODOX = 2 +EASTER_WESTERN = 3 + + +def easter(year, method=EASTER_WESTERN): + """ + This method was ported from the work done by GM Arts, + on top of the algorithm by Claus Tondering, which was + based in part on the algorithm of Ouding (1940), as + quoted in "Explanatory Supplement to the Astronomical + Almanac", P. Kenneth Seidelmann, editor. + + This algorithm implements three different Easter + calculation methods: + + 1. Original calculation in Julian calendar, valid in + dates after 326 AD + 2. Original method, with date converted to Gregorian + calendar, valid in years 1583 to 4099 + 3. Revised method, in Gregorian calendar, valid in + years 1583 to 4099 as well + + These methods are represented by the constants: + + * ``EASTER_JULIAN = 1`` + * ``EASTER_ORTHODOX = 2`` + * ``EASTER_WESTERN = 3`` + + The default method is method 3. + + More about the algorithm may be found at: + + `GM Arts: Easter Algorithms <http://www.gmarts.org/index.php?go=415>`_ + + and + + `The Calendar FAQ: Easter <https://www.tondering.dk/claus/cal/easter.php>`_ + + """ + + if not (1 <= method <= 3): + raise ValueError("invalid method") + + # g - Golden year - 1 + # c - Century + # h - (23 - Epact) mod 30 + # i - Number of days from March 21 to Paschal Full Moon + # j - Weekday for PFM (0=Sunday, etc) + # p - Number of days from March 21 to Sunday on or before PFM + # (-6 to 28 methods 1 & 3, to 56 for method 2) + # e - Extra days to add for method 2 (converting Julian + # date to Gregorian date) + + y = year + g = y % 19 + e = 0 + if method < 3: + # Old method + i = (19*g + 15) % 30 + j = (y + y//4 + i) % 7 + if method == 2: + # Extra dates to convert Julian to Gregorian date + e = 10 + if y > 1600: + e = e + y//100 - 16 - (y//100 - 16)//4 + else: + # New method + c = y//100 + h = (c - c//4 - (8*c + 13)//25 + 19*g + 15) % 30 + i = h - (h//28)*(1 - (h//28)*(29//(h + 1))*((21 - g)//11)) + j = (y + y//4 + i + 2 - c + c//4) % 7 + + # p can be from -6 to 56 corresponding to dates 22 March to 23 May + # (later dates apply to method 2, although 23 May never actually occurs) + p = i - j + e + d = 1 + (p + 27 + (p + 6)//40) % 31 + m = 3 + (p + 26)//30 + return datetime.date(int(y), int(m), int(d)) |