Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/dateutil/easter.py: 26%

1# -*- coding: utf-8 -*- 

2""" 

3This module offers a generic Easter computing method for any given year, using 

4Western, Orthodox or Julian algorithms. 

5""" 

6 

7import datetime 

8 

9__all__ = ["easter", "EASTER_JULIAN", "EASTER_ORTHODOX", "EASTER_WESTERN"] 

10 

11EASTER_JULIAN = 1 

12EASTER_ORTHODOX = 2 

13EASTER_WESTERN = 3 

14 

15 

16def easter(year, method=EASTER_WESTERN): 

17 """ 

18 This method was ported from the work done by GM Arts, 

19 on top of the algorithm by Claus Tondering, which was 

20 based in part on the algorithm of Ouding (1940), as 

21 quoted in "Explanatory Supplement to the Astronomical 

22 Almanac", P. Kenneth Seidelmann, editor. 

23 

24 This algorithm implements three different Easter 

25 calculation methods: 

26 

27 1. Original calculation in Julian calendar, valid in 

28 dates after 326 AD 

29 2. Original method, with date converted to Gregorian 

30 calendar, valid in years 1583 to 4099 

31 3. Revised method, in Gregorian calendar, valid in 

32 years 1583 to 4099 as well 

33 

34 These methods are represented by the constants: 

35 

36 * ``EASTER_JULIAN = 1`` 

37 * ``EASTER_ORTHODOX = 2`` 

38 * ``EASTER_WESTERN = 3`` 

39 

40 The default method is method 3. 

41 

42 More about the algorithm may be found at: 

43 

44 `GM Arts: Easter Algorithms <http://www.gmarts.org/index.php?go=415>`_ 

45 

46 and 

47 

48 `The Calendar FAQ: Easter <https://www.tondering.dk/claus/cal/easter.php>`_ 

49 

50 """ 

51 

52 if not (1 <= method <= 3): 

53 raise ValueError("invalid method") 

54 

55 # g - Golden year - 1 

56 # c - Century 

57 # h - (23 - Epact) mod 30 

58 # i - Number of days from March 21 to Paschal Full Moon 

59 # j - Weekday for PFM (0=Sunday, etc) 

60 # p - Number of days from March 21 to Sunday on or before PFM 

61 # (-6 to 28 methods 1 & 3, to 56 for method 2) 

62 # e - Extra days to add for method 2 (converting Julian 

63 # date to Gregorian date) 

64 

65 y = year 

66 g = y % 19 

67 e = 0 

68 if method < 3: 

69 # Old method 

70 i = (19*g + 15) % 30 

71 j = (y + y//4 + i) % 7 

72 if method == 2: 

73 # Extra dates to convert Julian to Gregorian date 

74 e = 10 

75 if y > 1600: 

76 e = e + y//100 - 16 - (y//100 - 16)//4 

77 else: 

78 # New method 

79 c = y//100 

80 h = (c - c//4 - (8*c + 13)//25 + 19*g + 15) % 30 

81 i = h - (h//28)*(1 - (h//28)*(29//(h + 1))*((21 - g)//11)) 

82 j = (y + y//4 + i + 2 - c + c//4) % 7 

83 

84 # p can be from -6 to 56 corresponding to dates 22 March to 23 May 

85 # (later dates apply to method 2, although 23 May never actually occurs) 

86 p = i - j + e 

87 d = 1 + (p + 27 + (p + 6)//40) % 31 

88 m = 3 + (p + 26)//30 

89 return datetime.date(int(y), int(m), int(d))