| from datetime import tzinfo, timedelta, datetime |
| |
| 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") |