jpayne@68: '''
jpayne@68: Reference tzinfo implementations from the Python docs.
jpayne@68: Used for testing against as they are only correct for the years
jpayne@68: 1987 to 2006. Do not use these for real code.
jpayne@68: '''
jpayne@68: 
jpayne@68: from datetime import tzinfo, timedelta, datetime
jpayne@68: from pytz import HOUR, ZERO, UTC
jpayne@68: 
jpayne@68: __all__ = [
jpayne@68:     'FixedOffset',
jpayne@68:     'LocalTimezone',
jpayne@68:     'USTimeZone',
jpayne@68:     'Eastern',
jpayne@68:     'Central',
jpayne@68:     'Mountain',
jpayne@68:     'Pacific',
jpayne@68:     'UTC'
jpayne@68: ]
jpayne@68: 
jpayne@68: 
jpayne@68: # A class building tzinfo objects for fixed-offset time zones.
jpayne@68: # Note that FixedOffset(0, "UTC") is a different way to build a
jpayne@68: # UTC tzinfo object.
jpayne@68: class FixedOffset(tzinfo):
jpayne@68:     """Fixed offset in minutes east from UTC."""
jpayne@68: 
jpayne@68:     def __init__(self, offset, name):
jpayne@68:         self.__offset = timedelta(minutes=offset)
jpayne@68:         self.__name = name
jpayne@68: 
jpayne@68:     def utcoffset(self, dt):
jpayne@68:         return self.__offset
jpayne@68: 
jpayne@68:     def tzname(self, dt):
jpayne@68:         return self.__name
jpayne@68: 
jpayne@68:     def dst(self, dt):
jpayne@68:         return ZERO
jpayne@68: 
jpayne@68: 
jpayne@68: import time as _time
jpayne@68: 
jpayne@68: STDOFFSET = timedelta(seconds=-_time.timezone)
jpayne@68: if _time.daylight:
jpayne@68:     DSTOFFSET = timedelta(seconds=-_time.altzone)
jpayne@68: else:
jpayne@68:     DSTOFFSET = STDOFFSET
jpayne@68: 
jpayne@68: DSTDIFF = DSTOFFSET - STDOFFSET
jpayne@68: 
jpayne@68: 
jpayne@68: # A class capturing the platform's idea of local time.
jpayne@68: class LocalTimezone(tzinfo):
jpayne@68: 
jpayne@68:     def utcoffset(self, dt):
jpayne@68:         if self._isdst(dt):
jpayne@68:             return DSTOFFSET
jpayne@68:         else:
jpayne@68:             return STDOFFSET
jpayne@68: 
jpayne@68:     def dst(self, dt):
jpayne@68:         if self._isdst(dt):
jpayne@68:             return DSTDIFF
jpayne@68:         else:
jpayne@68:             return ZERO
jpayne@68: 
jpayne@68:     def tzname(self, dt):
jpayne@68:         return _time.tzname[self._isdst(dt)]
jpayne@68: 
jpayne@68:     def _isdst(self, dt):
jpayne@68:         tt = (dt.year, dt.month, dt.day,
jpayne@68:               dt.hour, dt.minute, dt.second,
jpayne@68:               dt.weekday(), 0, -1)
jpayne@68:         stamp = _time.mktime(tt)
jpayne@68:         tt = _time.localtime(stamp)
jpayne@68:         return tt.tm_isdst > 0
jpayne@68: 
jpayne@68: Local = LocalTimezone()
jpayne@68: 
jpayne@68: 
jpayne@68: def first_sunday_on_or_after(dt):
jpayne@68:     days_to_go = 6 - dt.weekday()
jpayne@68:     if days_to_go:
jpayne@68:         dt += timedelta(days_to_go)
jpayne@68:     return dt
jpayne@68: 
jpayne@68: 
jpayne@68: # In the US, DST starts at 2am (standard time) on the first Sunday in April.
jpayne@68: DSTSTART = datetime(1, 4, 1, 2)
jpayne@68: # and ends at 2am (DST time; 1am standard time) on the last Sunday of Oct.
jpayne@68: # which is the first Sunday on or after Oct 25.
jpayne@68: DSTEND = datetime(1, 10, 25, 1)
jpayne@68: 
jpayne@68: 
jpayne@68: # A complete implementation of current DST rules for major US time zones.
jpayne@68: class USTimeZone(tzinfo):
jpayne@68: 
jpayne@68:     def __init__(self, hours, reprname, stdname, dstname):
jpayne@68:         self.stdoffset = timedelta(hours=hours)
jpayne@68:         self.reprname = reprname
jpayne@68:         self.stdname = stdname
jpayne@68:         self.dstname = dstname
jpayne@68: 
jpayne@68:     def __repr__(self):
jpayne@68:         return self.reprname
jpayne@68: 
jpayne@68:     def tzname(self, dt):
jpayne@68:         if self.dst(dt):
jpayne@68:             return self.dstname
jpayne@68:         else:
jpayne@68:             return self.stdname
jpayne@68: 
jpayne@68:     def utcoffset(self, dt):
jpayne@68:         return self.stdoffset + self.dst(dt)
jpayne@68: 
jpayne@68:     def dst(self, dt):
jpayne@68:         if dt is None or dt.tzinfo is None:
jpayne@68:             # An exception may be sensible here, in one or both cases.
jpayne@68:             # It depends on how you want to treat them.  The default
jpayne@68:             # fromutc() implementation (called by the default astimezone()
jpayne@68:             # implementation) passes a datetime with dt.tzinfo is self.
jpayne@68:             return ZERO
jpayne@68:         assert dt.tzinfo is self
jpayne@68: 
jpayne@68:         # Find first Sunday in April & the last in October.
jpayne@68:         start = first_sunday_on_or_after(DSTSTART.replace(year=dt.year))
jpayne@68:         end = first_sunday_on_or_after(DSTEND.replace(year=dt.year))
jpayne@68: 
jpayne@68:         # Can't compare naive to aware objects, so strip the timezone from
jpayne@68:         # dt first.
jpayne@68:         if start <= dt.replace(tzinfo=None) < end:
jpayne@68:             return HOUR
jpayne@68:         else:
jpayne@68:             return ZERO
jpayne@68: 
jpayne@68: Eastern = USTimeZone(-5, "Eastern", "EST", "EDT")
jpayne@68: Central = USTimeZone(-6, "Central", "CST", "CDT")
jpayne@68: Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
jpayne@68: Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")