Class _TZStr

Lib/zoneinfo/_zoneinfo.py:425–511

class _TZStr:
    __slots__ = (
        "std",
        "dst",
        "start",
        "end",
        "get_trans_info",
        "get_trans_info_fromutc",
        "dst_diff",
    )

    def __init__(
        self, std_abbr, std_offset, dst_abbr, dst_offset, start=None, end=None
    ):
        self.dst_diff = dst_offset - std_offset
        std_offset = _load_timedelta(std_offset)
        self.std = _ttinfo(
            utcoff=std_offset, dstoff=_load_timedelta(0), tzname=std_abbr
        )

        self.start = start
        self.end = end

        dst_offset = _load_timedelta(dst_offset)
        delta = _load_timedelta(self.dst_diff)
        self.dst = _ttinfo(utcoff=dst_offset, dstoff=delta, tzname=dst_abbr)

        # These are assertions because the constructor should only be called
        # by functions that would fail before passing start or end
        assert start is not None, "No transition start specified"
        assert end is not None, "No transition end specified"

        self.get_trans_info = self._get_trans_info
        self.get_trans_info_fromutc = self._get_trans_info_fromutc

    def transitions(self, year):
        start = self.start.year_to_epoch(year)
        end = self.end.year_to_epoch(year)
        return start, end

    def _get_trans_info(self, ts, year, fold):
        """Get the information about the current transition - tti"""
        start, end = self.transitions(year)

        # With fold = 0, the period (denominated in local time) with the
        # smaller offset starts at the end of the gap and ends at the end of
        # the fold; with fold = 1, it runs from the start of the gap to the
        # beginning of the fold.
        #
        # So in order to determine the DST boundaries we need to know both
        # the fold and whether DST is positive or negative (rare), and it
        # turns out that this boils down to fold XOR is_positive.
        if fold == (self.dst_diff >= 0):
            end -= self.dst_diff
        else:
            start += self.dst_diff

        if start < end: