22 lines
611 B
Python
22 lines
611 B
Python
"""Tolerant historical date parsing for the family archive."""
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import datetime
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def easter(year: int) -> datetime.date:
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"""Easter Sunday (Gregorian) via the Anonymous Gregorian / Butcher algorithm."""
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a = year % 19
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b = year // 100
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c = year % 100
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d = b // 4
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e = b % 4
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f = (b + 8) // 25
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g = (b - f + 1) // 3
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h = (19 * a + b - d - g + 15) % 30
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i = c // 4
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k = c % 4
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l = (32 + 2 * e + 2 * i - h - k) % 7
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m = (a + 11 * h + 22 * l) // 451
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month = (h + l - 7 * m + 114) // 31
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day = ((h + l - 7 * m + 114) % 31) + 1
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return datetime.date(year, month, day)
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