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When daylight time ends, an hour repeats on the local clock (for example, in US Eastern, the clock jumps from 1:59 back to 1:00 again). Times in the repeated hour are ambiguous. A tzinfo subclass that wants to play with astimezone() needs to treat times in the repeated hour as being standard time. astimezone() previously required that such times be treated as daylight time. There seems no killer argument either way, but Guido wants the standard-time version, and it does seem easier the new way to code both American (local-time based) and European (UTC-based) switch rules, and the astimezone() implementation is simpler.
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, 1)
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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 datetime 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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