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adf642038e
cases, plus even tougher tests of that. This implementation follows the correctness proof very closely, and should also be quicker (yes, I wrote the proof before the code, and the code proves the proof <wink>).
139 lines
3.6 KiB
Python
139 lines
3.6 KiB
Python
from datetime import tzinfo, timedelta, datetime
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ZERO = timedelta(0)
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HOUR = timedelta(hours=1)
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# A UTC class.
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class UTC(tzinfo):
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"""UTC"""
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def utcoffset(self, dt):
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return ZERO
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def tzname(self, dt):
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return "UTC"
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def dst(self, dt):
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return ZERO
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utc = UTC()
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# A class building tzinfo objects for fixed-offset time zones.
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# Note that FixedOffset(0, "UTC") is a different way to build a
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# UTC tzinfo object.
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class FixedOffset(tzinfo):
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"""Fixed offset in minutes east from UTC."""
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def __init__(self, offset, name):
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self.__offset = timdelta(minutes = offset)
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self.__name = name
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def utcoffset(self, dt):
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return self.__offset
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def tzname(self, dt):
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return self.__name
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def dst(self, dt):
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return ZERO
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# A class capturing the platform's idea of local time.
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import time as _time
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STDOFFSET = timedelta(seconds = -_time.timezone)
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if _time.daylight:
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DSTOFFSET = timedelta(seconds = -_time.altzone)
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else:
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DSTOFFSET = STDOFFSET
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DSTDIFF = DSTOFFSET - STDOFFSET
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class LocalTimezone(tzinfo):
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def utcoffset(self, dt):
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if self._isdst(dt):
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return DSTOFFSET
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else:
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return STDOFFSET
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def dst(self, dt):
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if self._isdst(dt):
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return DSTDIFF
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else:
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return ZERO
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def tzname(self, dt):
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return _time.tzname[self._isdst(dt)]
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def _isdst(self, dt):
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tt = (dt.year, dt.month, dt.day,
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dt.hour, dt.minute, dt.second,
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dt.weekday(), 0, -1)
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stamp = _time.mktime(tt)
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tt = _time.localtime(stamp)
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return tt.tm_isdst > 0
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Local = LocalTimezone()
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# A complete implementation of current DST rules for major US time zones.
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def first_sunday_on_or_after(dt):
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days_to_go = 6 - dt.weekday()
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if days_to_go:
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dt += timedelta(days_to_go)
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return dt
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# In the US, DST starts at 2am (standard time) on the first Sunday in April.
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DSTSTART = datetime(1, 4, 1, 2)
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# and ends at 2am (DST time; 1am standard time) on the last Sunday of Oct.
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# which is the first Sunday on or after Oct 25.
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DSTEND = datetime(1, 10, 25, 2)
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class USTimeZone(tzinfo):
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def __init__(self, hours, reprname, stdname, dstname):
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self.stdoffset = timedelta(hours=hours)
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self.reprname = reprname
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self.stdname = stdname
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self.dstname = dstname
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def __repr__(self):
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return self.reprname
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def tzname(self, dt):
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if self.dst(dt):
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return self.dstname
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else:
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return self.stdname
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def utcoffset(self, dt):
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return self.stdoffset + self.dst(dt)
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def dst(self, dt):
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if dt is None or dt.tzinfo is None:
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# An exception may be sensible here, in one or both cases.
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# It depends on how you want to treat them. The astimezone()
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# implementation always passes a datetimetz with
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# dt.tzinfo == self.
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return ZERO
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assert dt.tzinfo is self
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# Find first Sunday in April & the last in October.
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start = first_sunday_on_or_after(DSTSTART.replace(year=dt.year))
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end = first_sunday_on_or_after(DSTEND.replace(year=dt.year))
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# Can't compare naive to aware objects, so strip the timezone from
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# dt first.
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if start <= dt.replace(tzinfo=None) < end:
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return HOUR
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else:
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return ZERO
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Eastern = USTimeZone(-5, "Eastern", "EST", "EDT")
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Central = USTimeZone(-6, "Central", "CST", "CDT")
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Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
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Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")
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