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Diffstat (limited to 'Doc/includes/tzinfo_examples.py')
| -rw-r--r-- | Doc/includes/tzinfo_examples.py | 175 |
1 files changed, 175 insertions, 0 deletions
diff --git a/Doc/includes/tzinfo_examples.py b/Doc/includes/tzinfo_examples.py new file mode 100644 index 0000000..ae5a509 --- /dev/null +++ b/Doc/includes/tzinfo_examples.py @@ -0,0 +1,175 @@ +from datetime import tzinfo, timedelta, datetime, timezone + +ZERO = timedelta(0) +HOUR = timedelta(hours=1) +SECOND = timedelta(seconds=1) + +# A class capturing the platform's idea of local time. +# (May result in wrong values on historical times in +# timezones where UTC offset and/or the DST rules had +# changed in the past.) +import time as _time + +STDOFFSET = timedelta(seconds = -_time.timezone) +if _time.daylight: + DSTOFFSET = timedelta(seconds = -_time.altzone) +else: + DSTOFFSET = STDOFFSET + +DSTDIFF = DSTOFFSET - STDOFFSET + +class LocalTimezone(tzinfo): + + def fromutc(self, dt): + assert dt.tzinfo is self + stamp = (dt - datetime(1970, 1, 1, tzinfo=self)) // SECOND + args = _time.localtime(stamp)[:6] + dst_diff = DSTDIFF // SECOND + # Detect fold + fold = (args == _time.localtime(stamp - dst_diff)) + return datetime(*args, microsecond=dt.microsecond, + tzinfo=self, fold=fold) + + def utcoffset(self, dt): + if self._isdst(dt): + return DSTOFFSET + else: + return STDOFFSET + + def dst(self, dt): + if self._isdst(dt): + return DSTDIFF + else: + return ZERO + + def tzname(self, dt): + return _time.tzname[self._isdst(dt)] + + def _isdst(self, dt): + tt = (dt.year, dt.month, dt.day, + dt.hour, dt.minute, dt.second, + dt.weekday(), 0, 0) + stamp = _time.mktime(tt) + tt = _time.localtime(stamp) + return tt.tm_isdst > 0 + +Local = LocalTimezone() + + +# A complete implementation of current DST rules for major US time zones. + +def first_sunday_on_or_after(dt): + days_to_go = 6 - dt.weekday() + if days_to_go: + dt += timedelta(days_to_go) + return dt + + +# US DST Rules +# +# This is a simplified (i.e., wrong for a few cases) set of rules for US +# DST start and end times. For a complete and up-to-date set of DST rules +# and timezone definitions, visit the Olson Database (or try pytz): +# http://www.twinsun.com/tz/tz-link.htm +# http://sourceforge.net/projects/pytz/ (might not be up-to-date) +# +# In the US, since 2007, DST starts at 2am (standard time) on the second +# Sunday in March, which is the first Sunday on or after Mar 8. +DSTSTART_2007 = datetime(1, 3, 8, 2) +# and ends at 2am (DST time) on the first Sunday of Nov. +DSTEND_2007 = datetime(1, 11, 1, 2) +# From 1987 to 2006, DST used to start at 2am (standard time) on the first +# Sunday in April and to end at 2am (DST time) on the last +# Sunday of October, which is the first Sunday on or after Oct 25. +DSTSTART_1987_2006 = datetime(1, 4, 1, 2) +DSTEND_1987_2006 = datetime(1, 10, 25, 2) +# From 1967 to 1986, DST used to start at 2am (standard time) on the last +# Sunday in April (the one on or after April 24) and to end at 2am (DST time) +# on the last Sunday of October, which is the first Sunday +# on or after Oct 25. +DSTSTART_1967_1986 = datetime(1, 4, 24, 2) +DSTEND_1967_1986 = DSTEND_1987_2006 + +def us_dst_range(year): + # Find start and end times for US DST. For years before 1967, return + # start = end for no DST. + if 2006 < year: + dststart, dstend = DSTSTART_2007, DSTEND_2007 + elif 1986 < year < 2007: + dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006 + elif 1966 < year < 1987: + dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986 + else: + return (datetime(year, 1, 1), ) * 2 + + start = first_sunday_on_or_after(dststart.replace(year=year)) + end = first_sunday_on_or_after(dstend.replace(year=year)) + return start, end + + +class USTimeZone(tzinfo): + + def __init__(self, hours, reprname, stdname, dstname): + self.stdoffset = timedelta(hours=hours) + self.reprname = reprname + self.stdname = stdname + self.dstname = dstname + + def __repr__(self): + return self.reprname + + def tzname(self, dt): + if self.dst(dt): + return self.dstname + else: + return self.stdname + + def utcoffset(self, dt): + return self.stdoffset + self.dst(dt) + + def dst(self, dt): + if dt is None or dt.tzinfo is None: + # An exception may be sensible here, in one or both cases. + # It depends on how you want to treat them. The default + # fromutc() implementation (called by the default astimezone() + # implementation) passes a datetime with dt.tzinfo is self. + return ZERO + assert dt.tzinfo is self + start, end = us_dst_range(dt.year) + # Can't compare naive to aware objects, so strip the timezone from + # dt first. + dt = dt.replace(tzinfo=None) + if start + HOUR <= dt < end - HOUR: + # DST is in effect. + return HOUR + if end - HOUR <= dt < end: + # Fold (an ambiguous hour): use dt.fold to disambiguate. + return ZERO if dt.fold else HOUR + if start <= dt < start + HOUR: + # Gap (a non-existent hour): reverse the fold rule. + return HOUR if dt.fold else ZERO + # DST is off. + return ZERO + + def fromutc(self, dt): + assert dt.tzinfo is self + start, end = us_dst_range(dt.year) + start = start.replace(tzinfo=self) + end = end.replace(tzinfo=self) + std_time = dt + self.stdoffset + dst_time = std_time + HOUR + if end <= dst_time < end + HOUR: + # Repeated hour + return std_time.replace(fold=1) + if std_time < start or dst_time >= end: + # Standard time + return std_time + if start <= std_time < end - HOUR: + # Daylight saving time + return dst_time + + +Eastern = USTimeZone(-5, "Eastern", "EST", "EDT") +Central = USTimeZone(-6, "Central", "CST", "CDT") +Mountain = USTimeZone(-7, "Mountain", "MST", "MDT") +Pacific = USTimeZone(-8, "Pacific", "PST", "PDT") |