Function to return date of Easter for the given year

Question

So, here's a funny little programming challenge. I was writing a quick method to determine all the market holidays for a particular year, and then I started reading about Easter and discovered just how crazy* the logic is for determining its date--the first Sunday after the Paschal Full Moon following the spring equinox! Does anybody know of an existing function to calculate the date of Easter for a given year?

Granted, it's probably not all that hard to do; I just figured I'd ask in case somebody's already done this. (And that seems very likely.)

UPDATE: Actually, I'm really looking for the date of Good Friday (the Friday before Easter)... I just figured Easter would get me there. And since I'm in the U.S., I assume I'm looking for the Catholic Easter? But perhaps someone can correct me on that if I'm wrong.

_{*By "crazy" I meant, like, involved. Not anything offensive...}

Answer 1

Python: using dateutil's easter() function.

>>> from dateutil.easter import * >>> print easter(2010) 2010-04-04 >>> print easter(2011) 2011-04-24 

The functions gets, as an argument, the type of calculation you like:

EASTER_JULIAN   = 1 EASTER_ORTHODOX = 2 EASTER_WESTERN  = 3 

You can pick the one relevant to the US.

Reducing two days from the result would give you Good Friday:

>>> from datetime import timedelta >>> d = timedelta(days=-2) >>> easter(2011) datetime.date(2011, 4, 24) >>> easter(2011)+d datetime.date(2011, 4, 22) 

Oddly enough, someone was iterating this, and published the results in Wikipedia's article about the algorithm:

Answer 2

in SQL Server Easter Sunday would look like this, scroll down for Good Friday

CREATE FUNCTION dbo.GetEasterSunday  ( @Y INT )  RETURNS SMALLDATETIME  AS  BEGIN      DECLARE     @EpactCalc INT,           @PaschalDaysCalc INT,          @NumOfDaysToSunday INT,          @EasterMonth INT,          @EasterDay INT       SET @EpactCalc = (24 + 19 * (@Y % 19)) % 30      SET @PaschalDaysCalc = @EpactCalc - (@EpactCalc / 28)      SET @NumOfDaysToSunday = @PaschalDaysCalc - (          (@Y + @Y / 4 + @PaschalDaysCalc - 13) % 7      )       SET @EasterMonth = 3 + (@NumOfDaysToSunday + 40) / 44       SET @EasterDay = @NumOfDaysToSunday + 28 - (          31 * (@EasterMonth / 4)      )       RETURN      (          SELECT CONVERT          (  SMALLDATETIME,                   RTRIM(@Y)               + RIGHT('0'+RTRIM(@EasterMonth), 2)               + RIGHT('0'+RTRIM(@EasterDay), 2)           )      )   END  GO 

Good Friday is like this and it uses the Easter function above

CREATE FUNCTION dbo.GetGoodFriday  (      @Y INT  )  RETURNS SMALLDATETIME  AS  BEGIN      RETURN (SELECT dbo.GetEasterSunday(@Y) - 2)  END  GO 

From here: http://web.archive.org/web/20070611150639/http://sqlserver2000.databases.aspfaq.com/why-should-i-consider-using-an-auxiliary-calendar-table.html