扫码登录，获取cookies

backend/venv/Lib/site-packages/pytz/exceptions.py

@@ -0,0 +1,59 @@
+'''
+Custom exceptions raised by pytz.
+'''
+
+__all__ = [
+    'UnknownTimeZoneError', 'InvalidTimeError', 'AmbiguousTimeError',
+    'NonExistentTimeError',
+]
+
+
+class Error(Exception):
+    '''Base class for all exceptions raised by the pytz library'''
+
+
+class UnknownTimeZoneError(KeyError, Error):
+    '''Exception raised when pytz is passed an unknown timezone.
+
+    >>> isinstance(UnknownTimeZoneError(), LookupError)
+    True
+
+    This class is actually a subclass of KeyError to provide backwards
+    compatibility with code relying on the undocumented behavior of earlier
+    pytz releases.
+
+    >>> isinstance(UnknownTimeZoneError(), KeyError)
+    True
+
+    And also a subclass of pytz.exceptions.Error, as are other pytz
+    exceptions.
+
+    >>> isinstance(UnknownTimeZoneError(), Error)
+    True
+
+    '''
+    pass
+
+
+class InvalidTimeError(Error):
+    '''Base class for invalid time exceptions.'''
+
+
+class AmbiguousTimeError(InvalidTimeError):
+    '''Exception raised when attempting to create an ambiguous wallclock time.
+
+    At the end of a DST transition period, a particular wallclock time will
+    occur twice (once before the clocks are set back, once after). Both
+    possibilities may be correct, unless further information is supplied.
+
+    See DstTzInfo.normalize() for more info
+    '''
+
+
+class NonExistentTimeError(InvalidTimeError):
+    '''Exception raised when attempting to create a wallclock time that
+    cannot exist.
+
+    At the start of a DST transition period, the wallclock time jumps forward.
+    The instants jumped over never occur.
+    '''

backend/venv/Lib/site-packages/pytz/lazy.py

@@ -0,0 +1,172 @@
+from threading import RLock
+try:
+    from collections.abc import Mapping as DictMixin
+except ImportError:  # Python < 3.3
+    try:
+        from UserDict import DictMixin  # Python 2
+    except ImportError:  # Python 3.0-3.3
+        from collections import Mapping as DictMixin
+
+
+# With lazy loading, we might end up with multiple threads triggering
+# it at the same time. We need a lock.
+_fill_lock = RLock()
+
+
+class LazyDict(DictMixin):
+    """Dictionary populated on first use."""
+    data = None
+
+    def __getitem__(self, key):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return self.data[key.upper()]
+
+    def __contains__(self, key):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return key in self.data
+
+    def __iter__(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return iter(self.data)
+
+    def __len__(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return len(self.data)
+
+    def keys(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return self.data.keys()
+
+
+class LazyList(list):
+    """List populated on first use."""
+
+    _props = [
+        '__str__', '__repr__', '__unicode__',
+        '__hash__', '__sizeof__', '__cmp__',
+        '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__',
+        'append', 'count', 'index', 'extend', 'insert', 'pop', 'remove',
+        'reverse', 'sort', '__add__', '__radd__', '__iadd__', '__mul__',
+        '__rmul__', '__imul__', '__contains__', '__len__', '__nonzero__',
+        '__getitem__', '__setitem__', '__delitem__', '__iter__',
+        '__reversed__', '__getslice__', '__setslice__', '__delslice__']
+
+    def __new__(cls, fill_iter=None):
+
+        if fill_iter is None:
+            return list()
+
+        # We need a new class as we will be dynamically messing with its
+        # methods.
+        class LazyList(list):
+            pass
+
+        fill_iter = [fill_iter]
+
+        def lazy(name):
+            def _lazy(self, *args, **kw):
+                _fill_lock.acquire()
+                try:
+                    if len(fill_iter) > 0:
+                        list.extend(self, fill_iter.pop())
+                        for method_name in cls._props:
+                            delattr(LazyList, method_name)
+                finally:
+                    _fill_lock.release()
+                return getattr(list, name)(self, *args, **kw)
+            return _lazy
+
+        for name in cls._props:
+            setattr(LazyList, name, lazy(name))
+
+        new_list = LazyList()
+        return new_list
+
+# Not all versions of Python declare the same magic methods.
+# Filter out properties that don't exist in this version of Python
+# from the list.
+LazyList._props = [prop for prop in LazyList._props if hasattr(list, prop)]
+
+
+class LazySet(set):
+    """Set populated on first use."""
+
+    _props = (
+        '__str__', '__repr__', '__unicode__',
+        '__hash__', '__sizeof__', '__cmp__',
+        '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__',
+        '__contains__', '__len__', '__nonzero__',
+        '__getitem__', '__setitem__', '__delitem__', '__iter__',
+        '__sub__', '__and__', '__xor__', '__or__',
+        '__rsub__', '__rand__', '__rxor__', '__ror__',
+        '__isub__', '__iand__', '__ixor__', '__ior__',
+        'add', 'clear', 'copy', 'difference', 'difference_update',
+        'discard', 'intersection', 'intersection_update', 'isdisjoint',
+        'issubset', 'issuperset', 'pop', 'remove',
+        'symmetric_difference', 'symmetric_difference_update',
+        'union', 'update')
+
+    def __new__(cls, fill_iter=None):
+
+        if fill_iter is None:
+            return set()
+
+        class LazySet(set):
+            pass
+
+        fill_iter = [fill_iter]
+
+        def lazy(name):
+            def _lazy(self, *args, **kw):
+                _fill_lock.acquire()
+                try:
+                    if len(fill_iter) > 0:
+                        for i in fill_iter.pop():
+                            set.add(self, i)
+                        for method_name in cls._props:
+                            delattr(LazySet, method_name)
+                finally:
+                    _fill_lock.release()
+                return getattr(set, name)(self, *args, **kw)
+            return _lazy
+
+        for name in cls._props:
+            setattr(LazySet, name, lazy(name))
+
+        new_set = LazySet()
+        return new_set
+
+# Not all versions of Python declare the same magic methods.
+# Filter out properties that don't exist in this version of Python
+# from the list.
+LazySet._props = [prop for prop in LazySet._props if hasattr(set, prop)]

backend/venv/Lib/site-packages/pytz/reference.py

@@ -0,0 +1,140 @@
+'''
+Reference tzinfo implementations from the Python docs.
+Used for testing against as they are only correct for the years
+1987 to 2006. Do not use these for real code.
+'''
+
+from datetime import tzinfo, timedelta, datetime
+from pytz import HOUR, ZERO, UTC
+
+__all__ = [
+    'FixedOffset',
+    'LocalTimezone',
+    'USTimeZone',
+    'Eastern',
+    'Central',
+    'Mountain',
+    'Pacific',
+    'UTC'
+]
+
+
+# A class building tzinfo objects for fixed-offset time zones.
+# Note that FixedOffset(0, "UTC") is a different way to build a
+# UTC tzinfo object.
+class FixedOffset(tzinfo):
+    """Fixed offset in minutes east from UTC."""
+
+    def __init__(self, offset, name):
+        self.__offset = timedelta(minutes=offset)
+        self.__name = name
+
+    def utcoffset(self, dt):
+        return self.__offset
+
+    def tzname(self, dt):
+        return self.__name
+
+    def dst(self, dt):
+        return ZERO
+
+
+import time as _time
+
+STDOFFSET = timedelta(seconds=-_time.timezone)
+if _time.daylight:
+    DSTOFFSET = timedelta(seconds=-_time.altzone)
+else:
+    DSTOFFSET = STDOFFSET
+
+DSTDIFF = DSTOFFSET - STDOFFSET
+
+
+# A class capturing the platform's idea of local time.
+class LocalTimezone(tzinfo):
+
+    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, -1)
+        stamp = _time.mktime(tt)
+        tt = _time.localtime(stamp)
+        return tt.tm_isdst > 0
+
+Local = LocalTimezone()
+
+
+def first_sunday_on_or_after(dt):
+    days_to_go = 6 - dt.weekday()
+    if days_to_go:
+        dt += timedelta(days_to_go)
+    return dt
+
+
+# In the US, DST starts at 2am (standard time) on the first Sunday in April.
+DSTSTART = datetime(1, 4, 1, 2)
+# and ends at 2am (DST time; 1am standard time) on the last Sunday of Oct.
+# which is the first Sunday on or after Oct 25.
+DSTEND = datetime(1, 10, 25, 1)
+
+
+# A complete implementation of current DST rules for major US time zones.
+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
+
+        # Find first Sunday in April & the last in October.
+        start = first_sunday_on_or_after(DSTSTART.replace(year=dt.year))
+        end = first_sunday_on_or_after(DSTEND.replace(year=dt.year))
+
+        # Can't compare naive to aware objects, so strip the timezone from
+        # dt first.
+        if start <= dt.replace(tzinfo=None) < end:
+            return HOUR
+        else:
+            return ZERO
+
+Eastern = USTimeZone(-5, "Eastern", "EST", "EDT")
+Central = USTimeZone(-6, "Central", "CST", "CDT")
+Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
+Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")

backend/venv/Lib/site-packages/pytz/tzfile.py

@@ -0,0 +1,133 @@
+'''
+$Id: tzfile.py,v 1.8 2004/06/03 00:15:24 zenzen Exp $
+'''
+
+from datetime import datetime
+from struct import unpack, calcsize
+
+from pytz.tzinfo import StaticTzInfo, DstTzInfo, memorized_ttinfo
+from pytz.tzinfo import memorized_datetime, memorized_timedelta
+
+
+def _byte_string(s):
+    """Cast a string or byte string to an ASCII byte string."""
+    return s.encode('ASCII')
+
+_NULL = _byte_string('\0')
+
+
+def _std_string(s):
+    """Cast a string or byte string to an ASCII string."""
+    return str(s.decode('ASCII'))
+
+
+def build_tzinfo(zone, fp):
+    head_fmt = '>4s c 15x 6l'
+    head_size = calcsize(head_fmt)
+    (magic, format, ttisgmtcnt, ttisstdcnt, leapcnt, timecnt,
+        typecnt, charcnt) = unpack(head_fmt, fp.read(head_size))
+
+    # Make sure it is a tzfile(5) file
+    assert magic == _byte_string('TZif'), 'Got magic %s' % repr(magic)
+
+    # Read out the transition times, localtime indices and ttinfo structures.
+    data_fmt = '>%(timecnt)dl %(timecnt)dB %(ttinfo)s %(charcnt)ds' % dict(
+        timecnt=timecnt, ttinfo='lBB' * typecnt, charcnt=charcnt)
+    data_size = calcsize(data_fmt)
+    data = unpack(data_fmt, fp.read(data_size))
+
+    # make sure we unpacked the right number of values
+    assert len(data) == 2 * timecnt + 3 * typecnt + 1
+    transitions = [memorized_datetime(trans)
+                   for trans in data[:timecnt]]
+    lindexes = list(data[timecnt:2 * timecnt])
+    ttinfo_raw = data[2 * timecnt:-1]
+    tznames_raw = data[-1]
+    del data
+
+    # Process ttinfo into separate structs
+    ttinfo = []
+    tznames = {}
+    i = 0
+    while i < len(ttinfo_raw):
+        # have we looked up this timezone name yet?
+        tzname_offset = ttinfo_raw[i + 2]
+        if tzname_offset not in tznames:
+            nul = tznames_raw.find(_NULL, tzname_offset)
+            if nul < 0:
+                nul = len(tznames_raw)
+            tznames[tzname_offset] = _std_string(
+                tznames_raw[tzname_offset:nul])
+        ttinfo.append((ttinfo_raw[i],
+                       bool(ttinfo_raw[i + 1]),
+                       tznames[tzname_offset]))
+        i += 3
+
+    # Now build the timezone object
+    if len(ttinfo) == 1 or len(transitions) == 0:
+        ttinfo[0][0], ttinfo[0][2]
+        cls = type(zone, (StaticTzInfo,), dict(
+            zone=zone,
+            _utcoffset=memorized_timedelta(ttinfo[0][0]),
+            _tzname=ttinfo[0][2]))
+    else:
+        # Early dates use the first standard time ttinfo
+        i = 0
+        while ttinfo[i][1]:
+            i += 1
+        if ttinfo[i] == ttinfo[lindexes[0]]:
+            transitions[0] = datetime.min
+        else:
+            transitions.insert(0, datetime.min)
+            lindexes.insert(0, i)
+
+        # calculate transition info
+        transition_info = []
+        for i in range(len(transitions)):
+            inf = ttinfo[lindexes[i]]
+            utcoffset = inf[0]
+            if not inf[1]:
+                dst = 0
+            else:
+                for j in range(i - 1, -1, -1):
+                    prev_inf = ttinfo[lindexes[j]]
+                    if not prev_inf[1]:
+                        break
+                dst = inf[0] - prev_inf[0]  # dst offset
+
+                # Bad dst? Look further. DST > 24 hours happens when
+                # a timzone has moved across the international dateline.
+                if dst <= 0 or dst > 3600 * 3:
+                    for j in range(i + 1, len(transitions)):
+                        stdinf = ttinfo[lindexes[j]]
+                        if not stdinf[1]:
+                            dst = inf[0] - stdinf[0]
+                            if dst > 0:
+                                break  # Found a useful std time.
+
+            tzname = inf[2]
+
+            # Round utcoffset and dst to the nearest minute or the
+            # datetime library will complain. Conversions to these timezones
+            # might be up to plus or minus 30 seconds out, but it is
+            # the best we can do.
+            utcoffset = int((utcoffset + 30) // 60) * 60
+            dst = int((dst + 30) // 60) * 60
+            transition_info.append(memorized_ttinfo(utcoffset, dst, tzname))
+
+        cls = type(zone, (DstTzInfo,), dict(
+            zone=zone,
+            _utc_transition_times=transitions,
+            _transition_info=transition_info))
+
+    return cls()
+
+if __name__ == '__main__':
+    import os.path
+    from pprint import pprint
+    base = os.path.join(os.path.dirname(__file__), 'zoneinfo')
+    tz = build_tzinfo('Australia/Melbourne',
+                      open(os.path.join(base, 'Australia', 'Melbourne'), 'rb'))
+    tz = build_tzinfo('US/Eastern',
+                      open(os.path.join(base, 'US', 'Eastern'), 'rb'))
+    pprint(tz._utc_transition_times)

backend/venv/Lib/site-packages/pytz/tzinfo.py

@@ -0,0 +1,580 @@
+'''Base classes and helpers for building zone specific tzinfo classes'''
+
+from datetime import datetime, timedelta, tzinfo
+from bisect import bisect_right
+try:
+    set
+except NameError:
+    from sets import Set as set
+
+import pytz
+from pytz.exceptions import AmbiguousTimeError, NonExistentTimeError
+
+__all__ = []
+
+_timedelta_cache = {}
+
+
+def memorized_timedelta(seconds):
+    '''Create only one instance of each distinct timedelta'''
+    try:
+        return _timedelta_cache[seconds]
+    except KeyError:
+        delta = timedelta(seconds=seconds)
+        _timedelta_cache[seconds] = delta
+        return delta
+
+
+_epoch = datetime(1970, 1, 1, 0, 0) # datetime.utcfromtimestamp(0)
+_datetime_cache = {0: _epoch}
+
+
+def memorized_datetime(seconds):
+    '''Create only one instance of each distinct datetime'''
+    try:
+        return _datetime_cache[seconds]
+    except KeyError:
+        # NB. We can't just do datetime.fromtimestamp(seconds, tz=timezone.utc).replace(tzinfo=None)
+        # as this fails with negative values under Windows (Bug #90096)
+        dt = _epoch + timedelta(seconds=seconds)
+        _datetime_cache[seconds] = dt
+        return dt
+
+
+_ttinfo_cache = {}
+
+
+def memorized_ttinfo(*args):
+    '''Create only one instance of each distinct tuple'''
+    try:
+        return _ttinfo_cache[args]
+    except KeyError:
+        ttinfo = (
+            memorized_timedelta(args[0]),
+            memorized_timedelta(args[1]),
+            args[2]
+        )
+        _ttinfo_cache[args] = ttinfo
+        return ttinfo
+
+
+_notime = memorized_timedelta(0)
+
+
+def _to_seconds(td):
+    '''Convert a timedelta to seconds'''
+    return td.seconds + td.days * 24 * 60 * 60
+
+
+class BaseTzInfo(tzinfo):
+    # Overridden in subclass
+    _utcoffset = None
+    _tzname = None
+    zone = None
+
+    def __str__(self):
+        return self.zone
+
+
+class StaticTzInfo(BaseTzInfo):
+    '''A timezone that has a constant offset from UTC
+
+    These timezones are rare, as most locations have changed their
+    offset at some point in their history
+    '''
+    def fromutc(self, dt):
+        '''See datetime.tzinfo.fromutc'''
+        if dt.tzinfo is not None and dt.tzinfo is not self:
+            raise ValueError('fromutc: dt.tzinfo is not self')
+        return (dt + self._utcoffset).replace(tzinfo=self)
+
+    def utcoffset(self, dt, is_dst=None):
+        '''See datetime.tzinfo.utcoffset
+
+        is_dst is ignored for StaticTzInfo, and exists only to
+        retain compatibility with DstTzInfo.
+        '''
+        return self._utcoffset
+
+    def dst(self, dt, is_dst=None):
+        '''See datetime.tzinfo.dst
+
+        is_dst is ignored for StaticTzInfo, and exists only to
+        retain compatibility with DstTzInfo.
+        '''
+        return _notime
+
+    def tzname(self, dt, is_dst=None):
+        '''See datetime.tzinfo.tzname
+
+        is_dst is ignored for StaticTzInfo, and exists only to
+        retain compatibility with DstTzInfo.
+        '''
+        return self._tzname
+
+    def localize(self, dt, is_dst=False):
+        '''Convert naive time to local time'''
+        if dt.tzinfo is not None:
+            raise ValueError('Not naive datetime (tzinfo is already set)')
+        return dt.replace(tzinfo=self)
+
+    def normalize(self, dt, is_dst=False):
+        '''Correct the timezone information on the given datetime.
+
+        This is normally a no-op, as StaticTzInfo timezones never have
+        ambiguous cases to correct:
+
+        >>> from pytz import timezone
+        >>> gmt = timezone('GMT')
+        >>> isinstance(gmt, StaticTzInfo)
+        True
+        >>> dt = datetime(2011, 5, 8, 1, 2, 3, tzinfo=gmt)
+        >>> gmt.normalize(dt) is dt
+        True
+
+        The supported method of converting between timezones is to use
+        datetime.astimezone(). Currently normalize() also works:
+
+        >>> la = timezone('America/Los_Angeles')
+        >>> dt = la.localize(datetime(2011, 5, 7, 1, 2, 3))
+        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
+        >>> gmt.normalize(dt).strftime(fmt)
+        '2011-05-07 08:02:03 GMT (+0000)'
+        '''
+        if dt.tzinfo is self:
+            return dt
+        if dt.tzinfo is None:
+            raise ValueError('Naive time - no tzinfo set')
+        return dt.astimezone(self)
+
+    def __repr__(self):
+        return '<StaticTzInfo %r>' % (self.zone,)
+
+    def __reduce__(self):
+        # Special pickle to zone remains a singleton and to cope with
+        # database changes.
+        return pytz._p, (self.zone,)
+
+
+class DstTzInfo(BaseTzInfo):
+    '''A timezone that has a variable offset from UTC
+
+    The offset might change if daylight saving time comes into effect,
+    or at a point in history when the region decides to change their
+    timezone definition.
+    '''
+    # Overridden in subclass
+
+    # Sorted list of DST transition times, UTC
+    _utc_transition_times = None
+
+    # [(utcoffset, dstoffset, tzname)] corresponding to
+    # _utc_transition_times entries
+    _transition_info = None
+
+    zone = None
+
+    # Set in __init__
+
+    _tzinfos = None
+    _dst = None  # DST offset
+
+    def __init__(self, _inf=None, _tzinfos=None):
+        if _inf:
+            self._tzinfos = _tzinfos
+            self._utcoffset, self._dst, self._tzname = _inf
+        else:
+            _tzinfos = {}
+            self._tzinfos = _tzinfos
+            self._utcoffset, self._dst, self._tzname = (
+                self._transition_info[0])
+            _tzinfos[self._transition_info[0]] = self
+            for inf in self._transition_info[1:]:
+                if inf not in _tzinfos:
+                    _tzinfos[inf] = self.__class__(inf, _tzinfos)
+
+    def fromutc(self, dt):
+        '''See datetime.tzinfo.fromutc'''
+        if (dt.tzinfo is not None and
+                getattr(dt.tzinfo, '_tzinfos', None) is not self._tzinfos):
+            raise ValueError('fromutc: dt.tzinfo is not self')
+        dt = dt.replace(tzinfo=None)
+        idx = max(0, bisect_right(self._utc_transition_times, dt) - 1)
+        inf = self._transition_info[idx]
+        return (dt + inf[0]).replace(tzinfo=self._tzinfos[inf])
+
+    def normalize(self, dt):
+        '''Correct the timezone information on the given datetime
+
+        If date arithmetic crosses DST boundaries, the tzinfo
+        is not magically adjusted. This method normalizes the
+        tzinfo to the correct one.
+
+        To test, first we need to do some setup
+
+        >>> from pytz import timezone
+        >>> utc = timezone('UTC')
+        >>> eastern = timezone('US/Eastern')
+        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
+
+        We next create a datetime right on an end-of-DST transition point,
+        the instant when the wallclocks are wound back one hour.
+
+        >>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
+        >>> loc_dt = utc_dt.astimezone(eastern)
+        >>> loc_dt.strftime(fmt)
+        '2002-10-27 01:00:00 EST (-0500)'
+
+        Now, if we subtract a few minutes from it, note that the timezone
+        information has not changed.
+
+        >>> before = loc_dt - timedelta(minutes=10)
+        >>> before.strftime(fmt)
+        '2002-10-27 00:50:00 EST (-0500)'
+
+        But we can fix that by calling the normalize method
+
+        >>> before = eastern.normalize(before)
+        >>> before.strftime(fmt)
+        '2002-10-27 01:50:00 EDT (-0400)'
+
+        The supported method of converting between timezones is to use
+        datetime.astimezone(). Currently, normalize() also works:
+
+        >>> th = timezone('Asia/Bangkok')
+        >>> am = timezone('Europe/Amsterdam')
+        >>> dt = th.localize(datetime(2011, 5, 7, 1, 2, 3))
+        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
+        >>> am.normalize(dt).strftime(fmt)
+        '2011-05-06 20:02:03 CEST (+0200)'
+        '''
+        if dt.tzinfo is None:
+            raise ValueError('Naive time - no tzinfo set')
+
+        # Convert dt in localtime to UTC
+        offset = dt.tzinfo._utcoffset
+        dt = dt.replace(tzinfo=None)
+        dt = dt - offset
+        # convert it back, and return it
+        return self.fromutc(dt)
+
+    def localize(self, dt, is_dst=False):
+        '''Convert naive time to local time.
+
+        This method should be used to construct localtimes, rather
+        than passing a tzinfo argument to a datetime constructor.
+
+        is_dst is used to determine the correct timezone in the ambigous
+        period at the end of daylight saving time.
+
+        >>> from pytz import timezone
+        >>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
+        >>> amdam = timezone('Europe/Amsterdam')
+        >>> dt  = datetime(2004, 10, 31, 2, 0, 0)
+        >>> loc_dt1 = amdam.localize(dt, is_dst=True)
+        >>> loc_dt2 = amdam.localize(dt, is_dst=False)
+        >>> loc_dt1.strftime(fmt)
+        '2004-10-31 02:00:00 CEST (+0200)'
+        >>> loc_dt2.strftime(fmt)
+        '2004-10-31 02:00:00 CET (+0100)'
+        >>> str(loc_dt2 - loc_dt1)
+        '1:00:00'
+
+        Use is_dst=None to raise an AmbiguousTimeError for ambiguous
+        times at the end of daylight saving time
+
+        >>> try:
+        ...     loc_dt1 = amdam.localize(dt, is_dst=None)
+        ... except AmbiguousTimeError:
+        ...     print('Ambiguous')
+        Ambiguous
+
+        is_dst defaults to False
+
+        >>> amdam.localize(dt) == amdam.localize(dt, False)
+        True
+
+        is_dst is also used to determine the correct timezone in the
+        wallclock times jumped over at the start of daylight saving time.
+
+        >>> pacific = timezone('US/Pacific')
+        >>> dt = datetime(2008, 3, 9, 2, 0, 0)
+        >>> ploc_dt1 = pacific.localize(dt, is_dst=True)
+        >>> ploc_dt2 = pacific.localize(dt, is_dst=False)
+        >>> ploc_dt1.strftime(fmt)
+        '2008-03-09 02:00:00 PDT (-0700)'
+        >>> ploc_dt2.strftime(fmt)
+        '2008-03-09 02:00:00 PST (-0800)'
+        >>> str(ploc_dt2 - ploc_dt1)
+        '1:00:00'
+
+        Use is_dst=None to raise a NonExistentTimeError for these skipped
+        times.
+
+        >>> try:
+        ...     loc_dt1 = pacific.localize(dt, is_dst=None)
+        ... except NonExistentTimeError:
+        ...     print('Non-existent')
+        Non-existent
+        '''
+        if dt.tzinfo is not None:
+            raise ValueError('Not naive datetime (tzinfo is already set)')
+
+        # Find the two best possibilities.
+        possible_loc_dt = set()
+        for delta in [timedelta(days=-1), timedelta(days=1)]:
+            loc_dt = dt + delta
+            idx = max(0, bisect_right(
+                self._utc_transition_times, loc_dt) - 1)
+            inf = self._transition_info[idx]
+            tzinfo = self._tzinfos[inf]
+            loc_dt = tzinfo.normalize(dt.replace(tzinfo=tzinfo))
+            if loc_dt.replace(tzinfo=None) == dt:
+                possible_loc_dt.add(loc_dt)
+
+        if len(possible_loc_dt) == 1:
+            return possible_loc_dt.pop()
+
+        # If there are no possibly correct timezones, we are attempting
+        # to convert a time that never happened - the time period jumped
+        # during the start-of-DST transition period.
+        if len(possible_loc_dt) == 0:
+            # If we refuse to guess, raise an exception.
+            if is_dst is None:
+                raise NonExistentTimeError(dt)
+
+            # If we are forcing the pre-DST side of the DST transition, we
+            # obtain the correct timezone by winding the clock forward a few
+            # hours.
+            elif is_dst:
+                return self.localize(
+                    dt + timedelta(hours=6), is_dst=True) - timedelta(hours=6)
+
+            # If we are forcing the post-DST side of the DST transition, we
+            # obtain the correct timezone by winding the clock back.
+            else:
+                return self.localize(
+                    dt - timedelta(hours=6),
+                    is_dst=False) + timedelta(hours=6)
+
+        # If we get this far, we have multiple possible timezones - this
+        # is an ambiguous case occurring during the end-of-DST transition.
+
+        # If told to be strict, raise an exception since we have an
+        # ambiguous case
+        if is_dst is None:
+            raise AmbiguousTimeError(dt)
+
+        # Filter out the possiblilities that don't match the requested
+        # is_dst
+        filtered_possible_loc_dt = [
+            p for p in possible_loc_dt if bool(p.tzinfo._dst) == is_dst
+        ]
+
+        # Hopefully we only have one possibility left. Return it.
+        if len(filtered_possible_loc_dt) == 1:
+            return filtered_possible_loc_dt[0]
+
+        if len(filtered_possible_loc_dt) == 0:
+            filtered_possible_loc_dt = list(possible_loc_dt)
+
+        # If we get this far, we have in a wierd timezone transition
+        # where the clocks have been wound back but is_dst is the same
+        # in both (eg. Europe/Warsaw 1915 when they switched to CET).
+        # At this point, we just have to guess unless we allow more
+        # hints to be passed in (such as the UTC offset or abbreviation),
+        # but that is just getting silly.
+        #
+        # Choose the earliest (by UTC) applicable timezone if is_dst=True
+        # Choose the latest (by UTC) applicable timezone if is_dst=False
+        # i.e., behave like end-of-DST transition
+        dates = {}  # utc -> local
+        for local_dt in filtered_possible_loc_dt:
+            utc_time = (
+                local_dt.replace(tzinfo=None) - local_dt.tzinfo._utcoffset)
+            assert utc_time not in dates
+            dates[utc_time] = local_dt
+        return dates[[min, max][not is_dst](dates)]
+
+    def utcoffset(self, dt, is_dst=None):
+        '''See datetime.tzinfo.utcoffset
+
+        The is_dst parameter may be used to remove ambiguity during DST
+        transitions.
+
+        >>> from pytz import timezone
+        >>> tz = timezone('America/St_Johns')
+        >>> ambiguous = datetime(2009, 10, 31, 23, 30)
+
+        >>> str(tz.utcoffset(ambiguous, is_dst=False))
+        '-1 day, 20:30:00'
+
+        >>> str(tz.utcoffset(ambiguous, is_dst=True))
+        '-1 day, 21:30:00'
+
+        >>> try:
+        ...     tz.utcoffset(ambiguous)
+        ... except AmbiguousTimeError:
+        ...     print('Ambiguous')
+        Ambiguous
+
+        '''
+        if dt is None:
+            return None
+        elif dt.tzinfo is not self:
+            dt = self.localize(dt, is_dst)
+            return dt.tzinfo._utcoffset
+        else:
+            return self._utcoffset
+
+    def dst(self, dt, is_dst=None):
+        '''See datetime.tzinfo.dst
+
+        The is_dst parameter may be used to remove ambiguity during DST
+        transitions.
+
+        >>> from pytz import timezone
+        >>> tz = timezone('America/St_Johns')
+
+        >>> normal = datetime(2009, 9, 1)
+
+        >>> str(tz.dst(normal))
+        '1:00:00'
+        >>> str(tz.dst(normal, is_dst=False))
+        '1:00:00'
+        >>> str(tz.dst(normal, is_dst=True))
+        '1:00:00'
+
+        >>> ambiguous = datetime(2009, 10, 31, 23, 30)
+
+        >>> str(tz.dst(ambiguous, is_dst=False))
+        '0:00:00'
+        >>> str(tz.dst(ambiguous, is_dst=True))
+        '1:00:00'
+        >>> try:
+        ...     tz.dst(ambiguous)
+        ... except AmbiguousTimeError:
+        ...     print('Ambiguous')
+        Ambiguous
+
+        '''
+        if dt is None:
+            return None
+        elif dt.tzinfo is not self:
+            dt = self.localize(dt, is_dst)
+            return dt.tzinfo._dst
+        else:
+            return self._dst
+
+    def tzname(self, dt, is_dst=None):
+        '''See datetime.tzinfo.tzname
+
+        The is_dst parameter may be used to remove ambiguity during DST
+        transitions.
+
+        >>> from pytz import timezone
+        >>> tz = timezone('America/St_Johns')
+
+        >>> normal = datetime(2009, 9, 1)
+
+        >>> tz.tzname(normal)
+        'NDT'
+        >>> tz.tzname(normal, is_dst=False)
+        'NDT'
+        >>> tz.tzname(normal, is_dst=True)
+        'NDT'
+
+        >>> ambiguous = datetime(2009, 10, 31, 23, 30)
+
+        >>> tz.tzname(ambiguous, is_dst=False)
+        'NST'
+        >>> tz.tzname(ambiguous, is_dst=True)
+        'NDT'
+        >>> try:
+        ...     tz.tzname(ambiguous)
+        ... except AmbiguousTimeError:
+        ...     print('Ambiguous')
+        Ambiguous
+        '''
+        if dt is None:
+            return self.zone
+        elif dt.tzinfo is not self:
+            dt = self.localize(dt, is_dst)
+            return dt.tzinfo._tzname
+        else:
+            return self._tzname
+
+    def __repr__(self):
+        if self._dst:
+            dst = 'DST'
+        else:
+            dst = 'STD'
+        if self._utcoffset > _notime:
+            return '<DstTzInfo %r %s+%s %s>' % (
+                self.zone, self._tzname, self._utcoffset, dst
+            )
+        else:
+            return '<DstTzInfo %r %s%s %s>' % (
+                self.zone, self._tzname, self._utcoffset, dst
+            )
+
+    def __reduce__(self):
+        # Special pickle to zone remains a singleton and to cope with
+        # database changes.
+        return pytz._p, (
+            self.zone,
+            _to_seconds(self._utcoffset),
+            _to_seconds(self._dst),
+            self._tzname
+        )
+
+
+def unpickler(zone, utcoffset=None, dstoffset=None, tzname=None):
+    """Factory function for unpickling pytz tzinfo instances.
+
+    This is shared for both StaticTzInfo and DstTzInfo instances, because
+    database changes could cause a zones implementation to switch between
+    these two base classes and we can't break pickles on a pytz version
+    upgrade.
+    """
+    # Raises a KeyError if zone no longer exists, which should never happen
+    # and would be a bug.
+    tz = pytz.timezone(zone)
+
+    # A StaticTzInfo - just return it
+    if utcoffset is None:
+        return tz
+
+    # This pickle was created from a DstTzInfo. We need to
+    # determine which of the list of tzinfo instances for this zone
+    # to use in order to restore the state of any datetime instances using
+    # it correctly.
+    utcoffset = memorized_timedelta(utcoffset)
+    dstoffset = memorized_timedelta(dstoffset)
+    try:
+        return tz._tzinfos[(utcoffset, dstoffset, tzname)]
+    except KeyError:
+        # The particular state requested in this timezone no longer exists.
+        # This indicates a corrupt pickle, or the timezone database has been
+        # corrected violently enough to make this particular
+        # (utcoffset,dstoffset) no longer exist in the zone, or the
+        # abbreviation has been changed.
+        pass
+
+    # See if we can find an entry differing only by tzname. Abbreviations
+    # get changed from the initial guess by the database maintainers to
+    # match reality when this information is discovered.
+    for localized_tz in tz._tzinfos.values():
+        if (localized_tz._utcoffset == utcoffset and
+                localized_tz._dst == dstoffset):
+            return localized_tz
+
+    # This (utcoffset, dstoffset) information has been removed from the
+    # zone. Add it back. This might occur when the database maintainers have
+    # corrected incorrect information. datetime instances using this
+    # incorrect information will continue to do so, exactly as they were
+    # before being pickled. This is purely an overly paranoid safety net - I
+    # doubt this will ever been needed in real life.
+    inf = (utcoffset, dstoffset, tzname)
+    tz._tzinfos[inf] = tz.__class__(inf, tz._tzinfos)
+    return tz._tzinfos[inf]