e2ecdcfe33
Former-commit-id:a02aeb236c[formerly9f19e3f712] [formerlya02aeb236c[formerly9f19e3f712] [formerly06a8b51d6d[formerly 64fa9254b946eae7e61bbc3f513b7c3696c4f54f]]] Former-commit-id:06a8b51d6dFormer-commit-id:8e80217e59[formerly3360eb6c5f] Former-commit-id:377dcd10b9
92 lines
2.5 KiB
Python
Executable file
92 lines
2.5 KiB
Python
Executable file
"""
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Copyright (c) 2003-2005 Gustavo Niemeyer <gustavo@niemeyer.net>
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This module offers extensions to the standard python 2.3+
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datetime module.
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"""
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__author__ = "Gustavo Niemeyer <gustavo@niemeyer.net>"
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__license__ = "PSF License"
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import datetime
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__all__ = ["easter", "EASTER_JULIAN", "EASTER_ORTHODOX", "EASTER_WESTERN"]
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EASTER_JULIAN = 1
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EASTER_ORTHODOX = 2
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EASTER_WESTERN = 3
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def easter(year, method=EASTER_WESTERN):
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"""
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This method was ported from the work done by GM Arts,
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on top of the algorithm by Claus Tondering, which was
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based in part on the algorithm of Ouding (1940), as
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quoted in "Explanatory Supplement to the Astronomical
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Almanac", P. Kenneth Seidelmann, editor.
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This algorithm implements three different easter
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calculation methods:
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1 - Original calculation in Julian calendar, valid in
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dates after 326 AD
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2 - Original method, with date converted to Gregorian
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calendar, valid in years 1583 to 4099
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3 - Revised method, in Gregorian calendar, valid in
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years 1583 to 4099 as well
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These methods are represented by the constants:
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EASTER_JULIAN = 1
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EASTER_ORTHODOX = 2
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EASTER_WESTERN = 3
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The default method is method 3.
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More about the algorithm may be found at:
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http://users.chariot.net.au/~gmarts/eastalg.htm
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and
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http://www.tondering.dk/claus/calendar.html
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"""
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if not (1 <= method <= 3):
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raise ValueError, "invalid method"
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# g - Golden year - 1
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# c - Century
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# h - (23 - Epact) mod 30
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# i - Number of days from March 21 to Paschal Full Moon
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# j - Weekday for PFM (0=Sunday, etc)
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# p - Number of days from March 21 to Sunday on or before PFM
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# (-6 to 28 methods 1 & 3, to 56 for method 2)
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# e - Extra days to add for method 2 (converting Julian
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# date to Gregorian date)
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y = year
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g = y % 19
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e = 0
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if method < 3:
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# Old method
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i = (19*g+15)%30
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j = (y+y/4+i)%7
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if method == 2:
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# Extra dates to convert Julian to Gregorian date
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e = 10
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if y > 1600:
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e = e+y/100-16-(y/100-16)/4
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else:
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# New method
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c = y/100
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h = (c-c/4-(8*c+13)/25+19*g+15)%30
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i = h-(h/28)*(1-(h/28)*(29/(h+1))*((21-g)/11))
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j = (y+y/4+i+2-c+c/4)%7
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# p can be from -6 to 56 corresponding to dates 22 March to 23 May
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# (later dates apply to method 2, although 23 May never actually occurs)
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p = i-j+e
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d = 1+(p+27+(p+6)/40)%31
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m = 3+(p+26)/30
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return datetime.date(y,m,d)
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