Class _CalendarOffset

Lib/zoneinfo/_zoneinfo.py:547–624

class _CalendarOffset:
    __slots__ = ["m", "w", "d", "hour", "minute", "second"]

    _DAYS_BEFORE_MONTH = (
        -1,
        0,
        31,
        59,
        90,
        120,
        151,
        181,
        212,
        243,
        273,
        304,
        334,
    )

    def __init__(self, m, w, d, hour=2, minute=0, second=0):
        if not 1 <= m <= 12:
            raise ValueError("m must be in [1, 12]")

        if not 1 <= w <= 5:
            raise ValueError("w must be in [1, 5]")

        if not 0 <= d <= 6:
            raise ValueError("d must be in [0, 6]")

        self.m = m
        self.w = w
        self.d = d
        self.hour = hour
        self.minute = minute
        self.second = second

    @classmethod
    def _ymd2ord(cls, year, month, day):
        return (
            _post_epoch_days_before_year(year)
            + cls._DAYS_BEFORE_MONTH[month]
            + (month > 2 and calendar.isleap(year))
            + day
        )

    # TODO: These are not actually epoch dates as they are expressed in local time
    def year_to_epoch(self, year):
        """Calculates the datetime of the occurrence from the year"""
        # We know year and month, we need to convert w, d into day of month
        #
        # Week 1 is the first week in which day `d` (where 0 = Sunday) appears.
        # Week 5 represents the last occurrence of day `d`, so we need to know
        # the range of the month.
        first_day, days_in_month = calendar.monthrange(year, self.m)

        # This equation seems magical, so I'll break it down:
        # 1. calendar says 0 = Monday, POSIX says 0 = Sunday
        #    so we need first_day + 1 to get 1 = Monday -> 7 = Sunday,