jpayne@69: '''Base classes and helpers for building zone specific tzinfo classes'''
jpayne@69: 
jpayne@69: from datetime import datetime, timedelta, tzinfo
jpayne@69: from bisect import bisect_right
jpayne@69: try:
jpayne@69:     set
jpayne@69: except NameError:
jpayne@69:     from sets import Set as set
jpayne@69: 
jpayne@69: import pytz
jpayne@69: from pytz.exceptions import AmbiguousTimeError, NonExistentTimeError
jpayne@69: 
jpayne@69: __all__ = []
jpayne@69: 
jpayne@69: _timedelta_cache = {}
jpayne@69: 
jpayne@69: 
jpayne@69: def memorized_timedelta(seconds):
jpayne@69:     '''Create only one instance of each distinct timedelta'''
jpayne@69:     try:
jpayne@69:         return _timedelta_cache[seconds]
jpayne@69:     except KeyError:
jpayne@69:         delta = timedelta(seconds=seconds)
jpayne@69:         _timedelta_cache[seconds] = delta
jpayne@69:         return delta
jpayne@69: 
jpayne@69: 
jpayne@69: _epoch = datetime(1970, 1, 1, 0, 0) # datetime.utcfromtimestamp(0)
jpayne@69: _datetime_cache = {0: _epoch}
jpayne@69: 
jpayne@69: 
jpayne@69: def memorized_datetime(seconds):
jpayne@69:     '''Create only one instance of each distinct datetime'''
jpayne@69:     try:
jpayne@69:         return _datetime_cache[seconds]
jpayne@69:     except KeyError:
jpayne@69:         # NB. We can't just do datetime.fromtimestamp(seconds, tz=timezone.utc).replace(tzinfo=None)
jpayne@69:         # as this fails with negative values under Windows (Bug #90096)
jpayne@69:         dt = _epoch + timedelta(seconds=seconds)
jpayne@69:         _datetime_cache[seconds] = dt
jpayne@69:         return dt
jpayne@69: 
jpayne@69: 
jpayne@69: _ttinfo_cache = {}
jpayne@69: 
jpayne@69: 
jpayne@69: def memorized_ttinfo(*args):
jpayne@69:     '''Create only one instance of each distinct tuple'''
jpayne@69:     try:
jpayne@69:         return _ttinfo_cache[args]
jpayne@69:     except KeyError:
jpayne@69:         ttinfo = (
jpayne@69:             memorized_timedelta(args[0]),
jpayne@69:             memorized_timedelta(args[1]),
jpayne@69:             args[2]
jpayne@69:         )
jpayne@69:         _ttinfo_cache[args] = ttinfo
jpayne@69:         return ttinfo
jpayne@69: 
jpayne@69: 
jpayne@69: _notime = memorized_timedelta(0)
jpayne@69: 
jpayne@69: 
jpayne@69: def _to_seconds(td):
jpayne@69:     '''Convert a timedelta to seconds'''
jpayne@69:     return td.seconds + td.days * 24 * 60 * 60
jpayne@69: 
jpayne@69: 
jpayne@69: class BaseTzInfo(tzinfo):
jpayne@69:     # Overridden in subclass
jpayne@69:     _utcoffset = None
jpayne@69:     _tzname = None
jpayne@69:     zone = None
jpayne@69: 
jpayne@69:     def __str__(self):
jpayne@69:         return self.zone
jpayne@69: 
jpayne@69: 
jpayne@69: class StaticTzInfo(BaseTzInfo):
jpayne@69:     '''A timezone that has a constant offset from UTC
jpayne@69: 
jpayne@69:     These timezones are rare, as most locations have changed their
jpayne@69:     offset at some point in their history
jpayne@69:     '''
jpayne@69:     def fromutc(self, dt):
jpayne@69:         '''See datetime.tzinfo.fromutc'''
jpayne@69:         if dt.tzinfo is not None and dt.tzinfo is not self:
jpayne@69:             raise ValueError('fromutc: dt.tzinfo is not self')
jpayne@69:         return (dt + self._utcoffset).replace(tzinfo=self)
jpayne@69: 
jpayne@69:     def utcoffset(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.utcoffset
jpayne@69: 
jpayne@69:         is_dst is ignored for StaticTzInfo, and exists only to
jpayne@69:         retain compatibility with DstTzInfo.
jpayne@69:         '''
jpayne@69:         return self._utcoffset
jpayne@69: 
jpayne@69:     def dst(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.dst
jpayne@69: 
jpayne@69:         is_dst is ignored for StaticTzInfo, and exists only to
jpayne@69:         retain compatibility with DstTzInfo.
jpayne@69:         '''
jpayne@69:         return _notime
jpayne@69: 
jpayne@69:     def tzname(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.tzname
jpayne@69: 
jpayne@69:         is_dst is ignored for StaticTzInfo, and exists only to
jpayne@69:         retain compatibility with DstTzInfo.
jpayne@69:         '''
jpayne@69:         return self._tzname
jpayne@69: 
jpayne@69:     def localize(self, dt, is_dst=False):
jpayne@69:         '''Convert naive time to local time'''
jpayne@69:         if dt.tzinfo is not None:
jpayne@69:             raise ValueError('Not naive datetime (tzinfo is already set)')
jpayne@69:         return dt.replace(tzinfo=self)
jpayne@69: 
jpayne@69:     def normalize(self, dt, is_dst=False):
jpayne@69:         '''Correct the timezone information on the given datetime.
jpayne@69: 
jpayne@69:         This is normally a no-op, as StaticTzInfo timezones never have
jpayne@69:         ambiguous cases to correct:
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> gmt = timezone('GMT')
jpayne@69:         >>> isinstance(gmt, StaticTzInfo)
jpayne@69:         True
jpayne@69:         >>> dt = datetime(2011, 5, 8, 1, 2, 3, tzinfo=gmt)
jpayne@69:         >>> gmt.normalize(dt) is dt
jpayne@69:         True
jpayne@69: 
jpayne@69:         The supported method of converting between timezones is to use
jpayne@69:         datetime.astimezone(). Currently normalize() also works:
jpayne@69: 
jpayne@69:         >>> la = timezone('America/Los_Angeles')
jpayne@69:         >>> dt = la.localize(datetime(2011, 5, 7, 1, 2, 3))
jpayne@69:         >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
jpayne@69:         >>> gmt.normalize(dt).strftime(fmt)
jpayne@69:         '2011-05-07 08:02:03 GMT (+0000)'
jpayne@69:         '''
jpayne@69:         if dt.tzinfo is self:
jpayne@69:             return dt
jpayne@69:         if dt.tzinfo is None:
jpayne@69:             raise ValueError('Naive time - no tzinfo set')
jpayne@69:         return dt.astimezone(self)
jpayne@69: 
jpayne@69:     def __repr__(self):
jpayne@69:         return '<StaticTzInfo %r>' % (self.zone,)
jpayne@69: 
jpayne@69:     def __reduce__(self):
jpayne@69:         # Special pickle to zone remains a singleton and to cope with
jpayne@69:         # database changes.
jpayne@69:         return pytz._p, (self.zone,)
jpayne@69: 
jpayne@69: 
jpayne@69: class DstTzInfo(BaseTzInfo):
jpayne@69:     '''A timezone that has a variable offset from UTC
jpayne@69: 
jpayne@69:     The offset might change if daylight saving time comes into effect,
jpayne@69:     or at a point in history when the region decides to change their
jpayne@69:     timezone definition.
jpayne@69:     '''
jpayne@69:     # Overridden in subclass
jpayne@69: 
jpayne@69:     # Sorted list of DST transition times, UTC
jpayne@69:     _utc_transition_times = None
jpayne@69: 
jpayne@69:     # [(utcoffset, dstoffset, tzname)] corresponding to
jpayne@69:     # _utc_transition_times entries
jpayne@69:     _transition_info = None
jpayne@69: 
jpayne@69:     zone = None
jpayne@69: 
jpayne@69:     # Set in __init__
jpayne@69: 
jpayne@69:     _tzinfos = None
jpayne@69:     _dst = None  # DST offset
jpayne@69: 
jpayne@69:     def __init__(self, _inf=None, _tzinfos=None):
jpayne@69:         if _inf:
jpayne@69:             self._tzinfos = _tzinfos
jpayne@69:             self._utcoffset, self._dst, self._tzname = _inf
jpayne@69:         else:
jpayne@69:             _tzinfos = {}
jpayne@69:             self._tzinfos = _tzinfos
jpayne@69:             self._utcoffset, self._dst, self._tzname = (
jpayne@69:                 self._transition_info[0])
jpayne@69:             _tzinfos[self._transition_info[0]] = self
jpayne@69:             for inf in self._transition_info[1:]:
jpayne@69:                 if inf not in _tzinfos:
jpayne@69:                     _tzinfos[inf] = self.__class__(inf, _tzinfos)
jpayne@69: 
jpayne@69:     def fromutc(self, dt):
jpayne@69:         '''See datetime.tzinfo.fromutc'''
jpayne@69:         if (dt.tzinfo is not None and
jpayne@69:                 getattr(dt.tzinfo, '_tzinfos', None) is not self._tzinfos):
jpayne@69:             raise ValueError('fromutc: dt.tzinfo is not self')
jpayne@69:         dt = dt.replace(tzinfo=None)
jpayne@69:         idx = max(0, bisect_right(self._utc_transition_times, dt) - 1)
jpayne@69:         inf = self._transition_info[idx]
jpayne@69:         return (dt + inf[0]).replace(tzinfo=self._tzinfos[inf])
jpayne@69: 
jpayne@69:     def normalize(self, dt):
jpayne@69:         '''Correct the timezone information on the given datetime
jpayne@69: 
jpayne@69:         If date arithmetic crosses DST boundaries, the tzinfo
jpayne@69:         is not magically adjusted. This method normalizes the
jpayne@69:         tzinfo to the correct one.
jpayne@69: 
jpayne@69:         To test, first we need to do some setup
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> utc = timezone('UTC')
jpayne@69:         >>> eastern = timezone('US/Eastern')
jpayne@69:         >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
jpayne@69: 
jpayne@69:         We next create a datetime right on an end-of-DST transition point,
jpayne@69:         the instant when the wallclocks are wound back one hour.
jpayne@69: 
jpayne@69:         >>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
jpayne@69:         >>> loc_dt = utc_dt.astimezone(eastern)
jpayne@69:         >>> loc_dt.strftime(fmt)
jpayne@69:         '2002-10-27 01:00:00 EST (-0500)'
jpayne@69: 
jpayne@69:         Now, if we subtract a few minutes from it, note that the timezone
jpayne@69:         information has not changed.
jpayne@69: 
jpayne@69:         >>> before = loc_dt - timedelta(minutes=10)
jpayne@69:         >>> before.strftime(fmt)
jpayne@69:         '2002-10-27 00:50:00 EST (-0500)'
jpayne@69: 
jpayne@69:         But we can fix that by calling the normalize method
jpayne@69: 
jpayne@69:         >>> before = eastern.normalize(before)
jpayne@69:         >>> before.strftime(fmt)
jpayne@69:         '2002-10-27 01:50:00 EDT (-0400)'
jpayne@69: 
jpayne@69:         The supported method of converting between timezones is to use
jpayne@69:         datetime.astimezone(). Currently, normalize() also works:
jpayne@69: 
jpayne@69:         >>> th = timezone('Asia/Bangkok')
jpayne@69:         >>> am = timezone('Europe/Amsterdam')
jpayne@69:         >>> dt = th.localize(datetime(2011, 5, 7, 1, 2, 3))
jpayne@69:         >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
jpayne@69:         >>> am.normalize(dt).strftime(fmt)
jpayne@69:         '2011-05-06 20:02:03 CEST (+0200)'
jpayne@69:         '''
jpayne@69:         if dt.tzinfo is None:
jpayne@69:             raise ValueError('Naive time - no tzinfo set')
jpayne@69: 
jpayne@69:         # Convert dt in localtime to UTC
jpayne@69:         offset = dt.tzinfo._utcoffset
jpayne@69:         dt = dt.replace(tzinfo=None)
jpayne@69:         dt = dt - offset
jpayne@69:         # convert it back, and return it
jpayne@69:         return self.fromutc(dt)
jpayne@69: 
jpayne@69:     def localize(self, dt, is_dst=False):
jpayne@69:         '''Convert naive time to local time.
jpayne@69: 
jpayne@69:         This method should be used to construct localtimes, rather
jpayne@69:         than passing a tzinfo argument to a datetime constructor.
jpayne@69: 
jpayne@69:         is_dst is used to determine the correct timezone in the ambigous
jpayne@69:         period at the end of daylight saving time.
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
jpayne@69:         >>> amdam = timezone('Europe/Amsterdam')
jpayne@69:         >>> dt  = datetime(2004, 10, 31, 2, 0, 0)
jpayne@69:         >>> loc_dt1 = amdam.localize(dt, is_dst=True)
jpayne@69:         >>> loc_dt2 = amdam.localize(dt, is_dst=False)
jpayne@69:         >>> loc_dt1.strftime(fmt)
jpayne@69:         '2004-10-31 02:00:00 CEST (+0200)'
jpayne@69:         >>> loc_dt2.strftime(fmt)
jpayne@69:         '2004-10-31 02:00:00 CET (+0100)'
jpayne@69:         >>> str(loc_dt2 - loc_dt1)
jpayne@69:         '1:00:00'
jpayne@69: 
jpayne@69:         Use is_dst=None to raise an AmbiguousTimeError for ambiguous
jpayne@69:         times at the end of daylight saving time
jpayne@69: 
jpayne@69:         >>> try:
jpayne@69:         ...     loc_dt1 = amdam.localize(dt, is_dst=None)
jpayne@69:         ... except AmbiguousTimeError:
jpayne@69:         ...     print('Ambiguous')
jpayne@69:         Ambiguous
jpayne@69: 
jpayne@69:         is_dst defaults to False
jpayne@69: 
jpayne@69:         >>> amdam.localize(dt) == amdam.localize(dt, False)
jpayne@69:         True
jpayne@69: 
jpayne@69:         is_dst is also used to determine the correct timezone in the
jpayne@69:         wallclock times jumped over at the start of daylight saving time.
jpayne@69: 
jpayne@69:         >>> pacific = timezone('US/Pacific')
jpayne@69:         >>> dt = datetime(2008, 3, 9, 2, 0, 0)
jpayne@69:         >>> ploc_dt1 = pacific.localize(dt, is_dst=True)
jpayne@69:         >>> ploc_dt2 = pacific.localize(dt, is_dst=False)
jpayne@69:         >>> ploc_dt1.strftime(fmt)
jpayne@69:         '2008-03-09 02:00:00 PDT (-0700)'
jpayne@69:         >>> ploc_dt2.strftime(fmt)
jpayne@69:         '2008-03-09 02:00:00 PST (-0800)'
jpayne@69:         >>> str(ploc_dt2 - ploc_dt1)
jpayne@69:         '1:00:00'
jpayne@69: 
jpayne@69:         Use is_dst=None to raise a NonExistentTimeError for these skipped
jpayne@69:         times.
jpayne@69: 
jpayne@69:         >>> try:
jpayne@69:         ...     loc_dt1 = pacific.localize(dt, is_dst=None)
jpayne@69:         ... except NonExistentTimeError:
jpayne@69:         ...     print('Non-existent')
jpayne@69:         Non-existent
jpayne@69:         '''
jpayne@69:         if dt.tzinfo is not None:
jpayne@69:             raise ValueError('Not naive datetime (tzinfo is already set)')
jpayne@69: 
jpayne@69:         # Find the two best possibilities.
jpayne@69:         possible_loc_dt = set()
jpayne@69:         for delta in [timedelta(days=-1), timedelta(days=1)]:
jpayne@69:             loc_dt = dt + delta
jpayne@69:             idx = max(0, bisect_right(
jpayne@69:                 self._utc_transition_times, loc_dt) - 1)
jpayne@69:             inf = self._transition_info[idx]
jpayne@69:             tzinfo = self._tzinfos[inf]
jpayne@69:             loc_dt = tzinfo.normalize(dt.replace(tzinfo=tzinfo))
jpayne@69:             if loc_dt.replace(tzinfo=None) == dt:
jpayne@69:                 possible_loc_dt.add(loc_dt)
jpayne@69: 
jpayne@69:         if len(possible_loc_dt) == 1:
jpayne@69:             return possible_loc_dt.pop()
jpayne@69: 
jpayne@69:         # If there are no possibly correct timezones, we are attempting
jpayne@69:         # to convert a time that never happened - the time period jumped
jpayne@69:         # during the start-of-DST transition period.
jpayne@69:         if len(possible_loc_dt) == 0:
jpayne@69:             # If we refuse to guess, raise an exception.
jpayne@69:             if is_dst is None:
jpayne@69:                 raise NonExistentTimeError(dt)
jpayne@69: 
jpayne@69:             # If we are forcing the pre-DST side of the DST transition, we
jpayne@69:             # obtain the correct timezone by winding the clock forward a few
jpayne@69:             # hours.
jpayne@69:             elif is_dst:
jpayne@69:                 return self.localize(
jpayne@69:                     dt + timedelta(hours=6), is_dst=True) - timedelta(hours=6)
jpayne@69: 
jpayne@69:             # If we are forcing the post-DST side of the DST transition, we
jpayne@69:             # obtain the correct timezone by winding the clock back.
jpayne@69:             else:
jpayne@69:                 return self.localize(
jpayne@69:                     dt - timedelta(hours=6),
jpayne@69:                     is_dst=False) + timedelta(hours=6)
jpayne@69: 
jpayne@69:         # If we get this far, we have multiple possible timezones - this
jpayne@69:         # is an ambiguous case occurring during the end-of-DST transition.
jpayne@69: 
jpayne@69:         # If told to be strict, raise an exception since we have an
jpayne@69:         # ambiguous case
jpayne@69:         if is_dst is None:
jpayne@69:             raise AmbiguousTimeError(dt)
jpayne@69: 
jpayne@69:         # Filter out the possiblilities that don't match the requested
jpayne@69:         # is_dst
jpayne@69:         filtered_possible_loc_dt = [
jpayne@69:             p for p in possible_loc_dt if bool(p.tzinfo._dst) == is_dst
jpayne@69:         ]
jpayne@69: 
jpayne@69:         # Hopefully we only have one possibility left. Return it.
jpayne@69:         if len(filtered_possible_loc_dt) == 1:
jpayne@69:             return filtered_possible_loc_dt[0]
jpayne@69: 
jpayne@69:         if len(filtered_possible_loc_dt) == 0:
jpayne@69:             filtered_possible_loc_dt = list(possible_loc_dt)
jpayne@69: 
jpayne@69:         # If we get this far, we have in a wierd timezone transition
jpayne@69:         # where the clocks have been wound back but is_dst is the same
jpayne@69:         # in both (eg. Europe/Warsaw 1915 when they switched to CET).
jpayne@69:         # At this point, we just have to guess unless we allow more
jpayne@69:         # hints to be passed in (such as the UTC offset or abbreviation),
jpayne@69:         # but that is just getting silly.
jpayne@69:         #
jpayne@69:         # Choose the earliest (by UTC) applicable timezone if is_dst=True
jpayne@69:         # Choose the latest (by UTC) applicable timezone if is_dst=False
jpayne@69:         # i.e., behave like end-of-DST transition
jpayne@69:         dates = {}  # utc -> local
jpayne@69:         for local_dt in filtered_possible_loc_dt:
jpayne@69:             utc_time = (
jpayne@69:                 local_dt.replace(tzinfo=None) - local_dt.tzinfo._utcoffset)
jpayne@69:             assert utc_time not in dates
jpayne@69:             dates[utc_time] = local_dt
jpayne@69:         return dates[[min, max][not is_dst](dates)]
jpayne@69: 
jpayne@69:     def utcoffset(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.utcoffset
jpayne@69: 
jpayne@69:         The is_dst parameter may be used to remove ambiguity during DST
jpayne@69:         transitions.
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> tz = timezone('America/St_Johns')
jpayne@69:         >>> ambiguous = datetime(2009, 10, 31, 23, 30)
jpayne@69: 
jpayne@69:         >>> str(tz.utcoffset(ambiguous, is_dst=False))
jpayne@69:         '-1 day, 20:30:00'
jpayne@69: 
jpayne@69:         >>> str(tz.utcoffset(ambiguous, is_dst=True))
jpayne@69:         '-1 day, 21:30:00'
jpayne@69: 
jpayne@69:         >>> try:
jpayne@69:         ...     tz.utcoffset(ambiguous)
jpayne@69:         ... except AmbiguousTimeError:
jpayne@69:         ...     print('Ambiguous')
jpayne@69:         Ambiguous
jpayne@69: 
jpayne@69:         '''
jpayne@69:         if dt is None:
jpayne@69:             return None
jpayne@69:         elif dt.tzinfo is not self:
jpayne@69:             dt = self.localize(dt, is_dst)
jpayne@69:             return dt.tzinfo._utcoffset
jpayne@69:         else:
jpayne@69:             return self._utcoffset
jpayne@69: 
jpayne@69:     def dst(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.dst
jpayne@69: 
jpayne@69:         The is_dst parameter may be used to remove ambiguity during DST
jpayne@69:         transitions.
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> tz = timezone('America/St_Johns')
jpayne@69: 
jpayne@69:         >>> normal = datetime(2009, 9, 1)
jpayne@69: 
jpayne@69:         >>> str(tz.dst(normal))
jpayne@69:         '1:00:00'
jpayne@69:         >>> str(tz.dst(normal, is_dst=False))
jpayne@69:         '1:00:00'
jpayne@69:         >>> str(tz.dst(normal, is_dst=True))
jpayne@69:         '1:00:00'
jpayne@69: 
jpayne@69:         >>> ambiguous = datetime(2009, 10, 31, 23, 30)
jpayne@69: 
jpayne@69:         >>> str(tz.dst(ambiguous, is_dst=False))
jpayne@69:         '0:00:00'
jpayne@69:         >>> str(tz.dst(ambiguous, is_dst=True))
jpayne@69:         '1:00:00'
jpayne@69:         >>> try:
jpayne@69:         ...     tz.dst(ambiguous)
jpayne@69:         ... except AmbiguousTimeError:
jpayne@69:         ...     print('Ambiguous')
jpayne@69:         Ambiguous
jpayne@69: 
jpayne@69:         '''
jpayne@69:         if dt is None:
jpayne@69:             return None
jpayne@69:         elif dt.tzinfo is not self:
jpayne@69:             dt = self.localize(dt, is_dst)
jpayne@69:             return dt.tzinfo._dst
jpayne@69:         else:
jpayne@69:             return self._dst
jpayne@69: 
jpayne@69:     def tzname(self, dt, is_dst=None):
jpayne@69:         '''See datetime.tzinfo.tzname
jpayne@69: 
jpayne@69:         The is_dst parameter may be used to remove ambiguity during DST
jpayne@69:         transitions.
jpayne@69: 
jpayne@69:         >>> from pytz import timezone
jpayne@69:         >>> tz = timezone('America/St_Johns')
jpayne@69: 
jpayne@69:         >>> normal = datetime(2009, 9, 1)
jpayne@69: 
jpayne@69:         >>> tz.tzname(normal)
jpayne@69:         'NDT'
jpayne@69:         >>> tz.tzname(normal, is_dst=False)
jpayne@69:         'NDT'
jpayne@69:         >>> tz.tzname(normal, is_dst=True)
jpayne@69:         'NDT'
jpayne@69: 
jpayne@69:         >>> ambiguous = datetime(2009, 10, 31, 23, 30)
jpayne@69: 
jpayne@69:         >>> tz.tzname(ambiguous, is_dst=False)
jpayne@69:         'NST'
jpayne@69:         >>> tz.tzname(ambiguous, is_dst=True)
jpayne@69:         'NDT'
jpayne@69:         >>> try:
jpayne@69:         ...     tz.tzname(ambiguous)
jpayne@69:         ... except AmbiguousTimeError:
jpayne@69:         ...     print('Ambiguous')
jpayne@69:         Ambiguous
jpayne@69:         '''
jpayne@69:         if dt is None:
jpayne@69:             return self.zone
jpayne@69:         elif dt.tzinfo is not self:
jpayne@69:             dt = self.localize(dt, is_dst)
jpayne@69:             return dt.tzinfo._tzname
jpayne@69:         else:
jpayne@69:             return self._tzname
jpayne@69: 
jpayne@69:     def __repr__(self):
jpayne@69:         if self._dst:
jpayne@69:             dst = 'DST'
jpayne@69:         else:
jpayne@69:             dst = 'STD'
jpayne@69:         if self._utcoffset > _notime:
jpayne@69:             return '<DstTzInfo %r %s+%s %s>' % (
jpayne@69:                 self.zone, self._tzname, self._utcoffset, dst
jpayne@69:             )
jpayne@69:         else:
jpayne@69:             return '<DstTzInfo %r %s%s %s>' % (
jpayne@69:                 self.zone, self._tzname, self._utcoffset, dst
jpayne@69:             )
jpayne@69: 
jpayne@69:     def __reduce__(self):
jpayne@69:         # Special pickle to zone remains a singleton and to cope with
jpayne@69:         # database changes.
jpayne@69:         return pytz._p, (
jpayne@69:             self.zone,
jpayne@69:             _to_seconds(self._utcoffset),
jpayne@69:             _to_seconds(self._dst),
jpayne@69:             self._tzname
jpayne@69:         )
jpayne@69: 
jpayne@69: 
jpayne@69: def unpickler(zone, utcoffset=None, dstoffset=None, tzname=None):
jpayne@69:     """Factory function for unpickling pytz tzinfo instances.
jpayne@69: 
jpayne@69:     This is shared for both StaticTzInfo and DstTzInfo instances, because
jpayne@69:     database changes could cause a zones implementation to switch between
jpayne@69:     these two base classes and we can't break pickles on a pytz version
jpayne@69:     upgrade.
jpayne@69:     """
jpayne@69:     # Raises a KeyError if zone no longer exists, which should never happen
jpayne@69:     # and would be a bug.
jpayne@69:     tz = pytz.timezone(zone)
jpayne@69: 
jpayne@69:     # A StaticTzInfo - just return it
jpayne@69:     if utcoffset is None:
jpayne@69:         return tz
jpayne@69: 
jpayne@69:     # This pickle was created from a DstTzInfo. We need to
jpayne@69:     # determine which of the list of tzinfo instances for this zone
jpayne@69:     # to use in order to restore the state of any datetime instances using
jpayne@69:     # it correctly.
jpayne@69:     utcoffset = memorized_timedelta(utcoffset)
jpayne@69:     dstoffset = memorized_timedelta(dstoffset)
jpayne@69:     try:
jpayne@69:         return tz._tzinfos[(utcoffset, dstoffset, tzname)]
jpayne@69:     except KeyError:
jpayne@69:         # The particular state requested in this timezone no longer exists.
jpayne@69:         # This indicates a corrupt pickle, or the timezone database has been
jpayne@69:         # corrected violently enough to make this particular
jpayne@69:         # (utcoffset,dstoffset) no longer exist in the zone, or the
jpayne@69:         # abbreviation has been changed.
jpayne@69:         pass
jpayne@69: 
jpayne@69:     # See if we can find an entry differing only by tzname. Abbreviations
jpayne@69:     # get changed from the initial guess by the database maintainers to
jpayne@69:     # match reality when this information is discovered.
jpayne@69:     for localized_tz in tz._tzinfos.values():
jpayne@69:         if (localized_tz._utcoffset == utcoffset and
jpayne@69:                 localized_tz._dst == dstoffset):
jpayne@69:             return localized_tz
jpayne@69: 
jpayne@69:     # This (utcoffset, dstoffset) information has been removed from the
jpayne@69:     # zone. Add it back. This might occur when the database maintainers have
jpayne@69:     # corrected incorrect information. datetime instances using this
jpayne@69:     # incorrect information will continue to do so, exactly as they were
jpayne@69:     # before being pickled. This is purely an overly paranoid safety net - I
jpayne@69:     # doubt this will ever been needed in real life.
jpayne@69:     inf = (utcoffset, dstoffset, tzname)
jpayne@69:     tz._tzinfos[inf] = tz.__class__(inf, tz._tzinfos)
jpayne@69:     return tz._tzinfos[inf]