| 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192 |
- """
- Copyright (c) 2003-2007 Gustavo Niemeyer <gustavo@niemeyer.net>
- This module offers extensions to the standard python 2.3+
- datetime module.
- """
- __author__ = "Gustavo Niemeyer <gustavo@niemeyer.net>"
- __license__ = "PSF License"
- 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:
- http://users.chariot.net.au/~gmarts/eastalg.htm
- and
- http://www.tondering.dk/claus/calendar.html
- """
- 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))
|