Change improve getting the local timezone information.

CHANGES.md

@@ -174,6 +174,7 @@
 * Fix ensure downloaded eps are not shown on episode view
 * Fix allow propers to pp when show marked upgrade once
 * Fix never set episodes without airdate to wanted
+* Change improve getting the local timezone information
 
 [develop changelog]
 * Change send nzb data to NZBGet for Anizb instead of url

lib/pytz/exceptions.py

@@ -0,0 +1,48 @@
+'''
+Custom exceptions raised by pytz.
+'''
+
+__all__ = [
+    'UnknownTimeZoneError', 'InvalidTimeError', 'AmbiguousTimeError',
+    'NonExistentTimeError',
+    ]
+
+
+class UnknownTimeZoneError(KeyError):
+    '''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
+    '''
+    pass
+
+
+class InvalidTimeError(Exception):
+    '''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.
+    '''

lib/pytz/lazy.py

@@ -0,0 +1,168 @@
+from threading import RLock
+try:
+    from UserDict import DictMixin
+except ImportError:
+    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)]

lib/pytz/reference.py

@@ -0,0 +1,127 @@
+'''
+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 utc, UTC, HOUR, ZERO
+
+# 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
+
+# A class capturing the platform's idea of local time.
+
+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 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()
+
+# 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
+
+# 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)
+
+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")
+

lib/pytz/tests/test_docs.py

@@ -0,0 +1,34 @@
+# -*- coding: ascii -*-
+
+from doctest import DocFileSuite
+import unittest, os.path, sys
+
+THIS_DIR = os.path.dirname(__file__)
+
+README = os.path.join(THIS_DIR, os.pardir, os.pardir, 'README.txt')
+
+
+class DocumentationTestCase(unittest.TestCase):
+    def test_readme_encoding(self):
+        '''Confirm the README.txt is pure ASCII.'''
+        f = open(README, 'rb')
+        try:
+            f.read().decode('ASCII')
+        finally:
+            f.close()
+
+
+def test_suite():
+    "For the Z3 test runner"
+    return unittest.TestSuite((
+        DocumentationTestCase('test_readme_encoding'),
+        DocFileSuite(os.path.join(os.pardir, os.pardir, 'README.txt'))))
+
+
+if __name__ == '__main__':
+    sys.path.insert(0, os.path.abspath(os.path.join(
+        THIS_DIR, os.pardir, os.pardir
+        )))
+    unittest.main(defaultTest='test_suite')
+
+

lib/pytz/tests/test_lazy.py

@@ -0,0 +1,313 @@
+from operator import *
+import os.path
+import sys
+import unittest
+import warnings
+
+
+if __name__ == '__main__':
+    # Only munge path if invoked as a script. Testrunners should have setup
+    # the paths already
+    sys.path.insert(0, os.path.abspath(os.path.join(os.pardir, os.pardir)))
+
+
+from pytz.lazy import LazyList, LazySet
+
+
+class LazyListTestCase(unittest.TestCase):
+    initial_data = [3,2,1]
+
+    def setUp(self):
+        self.base = [3, 2, 1]
+        self.lesser = [2, 1, 0]
+        self.greater = [4, 3, 2]
+
+        self.lazy = LazyList(iter(list(self.base)))
+
+    def test_unary_ops(self):
+        unary_ops = [str, repr, len, bool, not_]
+        try:
+            unary_ops.append(unicode)
+        except NameError:
+            pass  # unicode no longer exists in Python 3.
+
+        for op in unary_ops:
+            self.assertEqual(
+                op(self.lazy),
+                op(self.base), str(op))
+
+    def test_binary_ops(self):
+        binary_ops = [eq, ge, gt, le, lt, ne, add, concat]
+        try:
+            binary_ops.append(cmp)
+        except NameError:
+            pass  # cmp no longer exists in Python 3.
+
+        for op in binary_ops:
+            self.assertEqual(
+                op(self.lazy, self.lazy),
+                op(self.base, self.base), str(op))
+            for other in [self.base, self.lesser, self.greater]:
+                self.assertEqual(
+                    op(self.lazy, other),
+                    op(self.base, other), '%s %s' % (op, other))
+                self.assertEqual(
+                    op(other, self.lazy),
+                    op(other, self.base), '%s %s' % (op, other))
+
+        # Multiplication
+        self.assertEqual(self.lazy * 3, self.base * 3)
+        self.assertEqual(3 * self.lazy, 3 * self.base)
+
+        # Contains
+        self.assertTrue(2 in self.lazy)
+        self.assertFalse(42 in self.lazy)
+
+    def test_iadd(self):
+        self.lazy += [1]
+        self.base += [1]
+        self.assertEqual(self.lazy, self.base)
+
+    def test_bool(self):
+        self.assertTrue(bool(self.lazy))
+        self.assertFalse(bool(LazyList()))
+        self.assertFalse(bool(LazyList(iter([]))))
+
+    def test_hash(self):
+        self.assertRaises(TypeError, hash, self.lazy)
+
+    def test_isinstance(self):
+        self.assertTrue(isinstance(self.lazy, list))
+        self.assertFalse(isinstance(self.lazy, tuple))
+
+    def test_callable(self):
+        try:
+            callable
+        except NameError:
+            return  # No longer exists with Python 3.
+        self.assertFalse(callable(self.lazy))
+
+    def test_append(self):
+        self.base.append('extra')
+        self.lazy.append('extra')
+        self.assertEqual(self.lazy, self.base)
+
+    def test_count(self):
+        self.assertEqual(self.lazy.count(2), 1)
+
+    def test_index(self):
+        self.assertEqual(self.lazy.index(2), 1)
+
+    def test_extend(self):
+        self.base.extend([6, 7])
+        self.lazy.extend([6, 7])
+        self.assertEqual(self.lazy, self.base)
+
+    def test_insert(self):
+        self.base.insert(0, 'ping')
+        self.lazy.insert(0, 'ping')
+        self.assertEqual(self.lazy, self.base)
+
+    def test_pop(self):
+        self.assertEqual(self.lazy.pop(), self.base.pop())
+        self.assertEqual(self.lazy, self.base)
+
+    def test_remove(self):
+        self.base.remove(2)
+        self.lazy.remove(2)
+        self.assertEqual(self.lazy, self.base)
+
+    def test_reverse(self):
+        self.base.reverse()
+        self.lazy.reverse()
+        self.assertEqual(self.lazy, self.base)
+
+    def test_reversed(self):
+        self.assertEqual(list(reversed(self.lazy)), list(reversed(self.base)))
+
+    def test_sort(self):
+        self.base.sort()
+        self.assertNotEqual(self.lazy, self.base, 'Test data already sorted')
+        self.lazy.sort()
+        self.assertEqual(self.lazy, self.base)
+
+    def test_sorted(self):
+        self.assertEqual(sorted(self.lazy), sorted(self.base))
+
+    def test_getitem(self):
+        for idx in range(-len(self.base), len(self.base)):
+            self.assertEqual(self.lazy[idx], self.base[idx])
+
+    def test_setitem(self):
+        for idx in range(-len(self.base), len(self.base)):
+            self.base[idx] = idx + 1000
+            self.assertNotEqual(self.lazy, self.base)
+            self.lazy[idx] = idx + 1000
+            self.assertEqual(self.lazy, self.base)
+
+    def test_delitem(self):
+        del self.base[0]
+        self.assertNotEqual(self.lazy, self.base)
+        del self.lazy[0]
+        self.assertEqual(self.lazy, self.base)
+
+        del self.base[-2]
+        self.assertNotEqual(self.lazy, self.base)
+        del self.lazy[-2]
+        self.assertEqual(self.lazy, self.base)
+
+    def test_iter(self):
+        self.assertEqual(list(iter(self.lazy)), list(iter(self.base)))
+
+    def test_getslice(self):
+        for i in range(-len(self.base), len(self.base)):
+            for j in range(-len(self.base), len(self.base)):
+                for step in [-1, 1]:
+                    self.assertEqual(self.lazy[i:j:step], self.base[i:j:step])
+
+    def test_setslice(self):
+        for i in range(-len(self.base), len(self.base)):
+            for j in range(-len(self.base), len(self.base)):
+                for step in [-1, 1]:
+                    replacement = range(0, len(self.base[i:j:step]))
+                    self.base[i:j:step] = replacement
+                    self.lazy[i:j:step] = replacement
+                    self.assertEqual(self.lazy, self.base)
+
+    def test_delslice(self):
+        del self.base[0:1]
+        del self.lazy[0:1]
+        self.assertEqual(self.lazy, self.base)
+
+        del self.base[-1:1:-1]
+        del self.lazy[-1:1:-1]
+        self.assertEqual(self.lazy, self.base)
+
+
+class LazySetTestCase(unittest.TestCase):
+    initial_data = set([3,2,1])
+
+    def setUp(self):
+        self.base = set([3, 2, 1])
+        self.lazy = LazySet(iter(set(self.base)))
+
+    def test_unary_ops(self):
+        # These ops just need to work.
+        unary_ops = [str, repr]
+        try:
+            unary_ops.append(unicode)
+        except NameError:
+            pass  # unicode no longer exists in Python 3.
+
+        for op in unary_ops:
+            op(self.lazy)  # These ops just need to work.
+
+        # These ops should return identical values as a real set.
+        unary_ops = [len, bool, not_]
+
+        for op in unary_ops:
+            self.assertEqual(
+                op(self.lazy),
+                op(self.base), '%s(lazy) == %r' % (op, op(self.lazy)))
+
+    def test_binary_ops(self):
+        binary_ops = [eq, ge, gt, le, lt, ne, sub, and_, or_, xor]
+        try:
+            binary_ops.append(cmp)
+        except NameError:
+            pass  # cmp no longer exists in Python 3.
+
+        for op in binary_ops:
+            self.assertEqual(
+                op(self.lazy, self.lazy),
+                op(self.base, self.base), str(op))
+            self.assertEqual(
+                op(self.lazy, self.base),
+                op(self.base, self.base), str(op))
+            self.assertEqual(
+                op(self.base, self.lazy),
+                op(self.base, self.base), str(op))
+
+        # Contains
+        self.assertTrue(2 in self.lazy)
+        self.assertFalse(42 in self.lazy)
+
+    def test_iops(self):
+        try:
+            iops = [isub, iand, ior, ixor]
+        except NameError:
+            return  # Don't exist in older Python versions.
+        for op in iops:
+            # Mutating operators, so make fresh copies.
+            lazy = LazySet(self.base)
+            base = self.base.copy()
+            op(lazy, set([1]))
+            op(base, set([1]))
+            self.assertEqual(lazy, base, str(op))
+
+    def test_bool(self):
+        self.assertTrue(bool(self.lazy))
+        self.assertFalse(bool(LazySet()))
+        self.assertFalse(bool(LazySet(iter([]))))
+
+    def test_hash(self):
+        self.assertRaises(TypeError, hash, self.lazy)
+
+    def test_isinstance(self):
+        self.assertTrue(isinstance(self.lazy, set))
+
+    def test_callable(self):
+        try:
+            callable
+        except NameError:
+            return  # No longer exists with Python 3.
+        self.assertFalse(callable(self.lazy))
+
+    def test_add(self):
+        self.base.add('extra')
+        self.lazy.add('extra')
+        self.assertEqual(self.lazy, self.base)
+
+    def test_copy(self):
+        self.assertEqual(self.lazy.copy(), self.base)
+
+    def test_method_ops(self):
+        ops = [
+            'difference', 'intersection', 'isdisjoint',
+            'issubset', 'issuperset', 'symmetric_difference', 'union',
+            'difference_update', 'intersection_update',
+            'symmetric_difference_update', 'update']
+        for op in ops:
+            if not hasattr(set, op):
+                continue  # Not in this version of Python.
+            # Make a copy, as some of the ops are mutating.
+            lazy = LazySet(set(self.base))
+            base = set(self.base)
+            self.assertEqual(
+                getattr(self.lazy, op)(set([1])),
+                getattr(self.base, op)(set([1])), op)
+            self.assertEqual(self.lazy, self.base, op)
+
+    def test_discard(self):
+        self.base.discard(1)
+        self.assertNotEqual(self.lazy, self.base)
+        self.lazy.discard(1)
+        self.assertEqual(self.lazy, self.base)
+
+    def test_pop(self):
+        self.assertEqual(self.lazy.pop(), self.base.pop())
+        self.assertEqual(self.lazy, self.base)
+
+    def test_remove(self):
+        self.base.remove(2)
+        self.lazy.remove(2)
+        self.assertEqual(self.lazy, self.base)
+
+    def test_clear(self):
+        self.lazy.clear()
+        self.assertEqual(self.lazy, set())
+
+
+if __name__ == '__main__':
+    warnings.simplefilter("error") # Warnings should be fatal in tests.
+    unittest.main()

lib/pytz/tests/test_tzinfo.py

@@ -0,0 +1,843 @@
+# -*- coding: ascii -*-
+
+import sys, os, os.path
+import unittest, doctest
+try:
+    import cPickle as pickle
+except ImportError:
+    import pickle
+from datetime import datetime, time, timedelta, tzinfo
+import warnings
+
+if __name__ == '__main__':
+    # Only munge path if invoked as a script. Testrunners should have setup
+    # the paths already
+    sys.path.insert(0, os.path.abspath(os.path.join(os.pardir, os.pardir)))
+
+import pytz
+from pytz import reference
+from pytz.tzfile import _byte_string
+from pytz.tzinfo import DstTzInfo, StaticTzInfo
+
+# I test for expected version to ensure the correct version of pytz is
+# actually being tested.
+EXPECTED_VERSION='2016.6.1'
+EXPECTED_OLSON_VERSION='2016f'
+
+fmt = '%Y-%m-%d %H:%M:%S %Z%z'
+
+NOTIME = timedelta(0)
+
+# GMT is a tzinfo.StaticTzInfo--the class we primarily want to test--while
+# UTC is reference implementation.  They both have the same timezone meaning.
+UTC = pytz.timezone('UTC')
+GMT = pytz.timezone('GMT')
+assert isinstance(GMT, StaticTzInfo), 'GMT is no longer a StaticTzInfo'
+
+def prettydt(dt):
+    """datetime as a string using a known format.
+
+    We don't use strftime as it doesn't handle years earlier than 1900
+    per http://bugs.python.org/issue1777412
+    """
+    if dt.utcoffset() >= timedelta(0):
+        offset = '+%s' % (dt.utcoffset(),)
+    else:
+        offset = '-%s' % (-1 * dt.utcoffset(),)
+    return '%04d-%02d-%02d %02d:%02d:%02d %s %s' % (
+        dt.year, dt.month, dt.day,
+        dt.hour, dt.minute, dt.second,
+        dt.tzname(), offset)
+
+
+try:
+    unicode
+except NameError:
+    # Python 3.x doesn't have unicode(), making writing code
+    # for Python 2.3 and Python 3.x a pain.
+    unicode = str
+
+
+class BasicTest(unittest.TestCase):
+
+    def testVersion(self):
+        # Ensuring the correct version of pytz has been loaded
+        self.assertEqual(EXPECTED_VERSION, pytz.__version__,
+                'Incorrect pytz version loaded. Import path is stuffed '
+                'or this test needs updating. (Wanted %s, got %s)'
+                % (EXPECTED_VERSION, pytz.__version__))
+
+        self.assertEqual(EXPECTED_OLSON_VERSION, pytz.OLSON_VERSION,
+                'Incorrect pytz version loaded. Import path is stuffed '
+                'or this test needs updating. (Wanted %s, got %s)'
+                % (EXPECTED_OLSON_VERSION, pytz.OLSON_VERSION))
+
+    def testGMT(self):
+        now = datetime.now(tz=GMT)
+        self.assertTrue(now.utcoffset() == NOTIME)
+        self.assertTrue(now.dst() == NOTIME)
+        self.assertTrue(now.timetuple() == now.utctimetuple())
+        self.assertTrue(now==now.replace(tzinfo=UTC))
+
+    def testReferenceUTC(self):
+        now = datetime.now(tz=UTC)
+        self.assertTrue(now.utcoffset() == NOTIME)
+        self.assertTrue(now.dst() == NOTIME)
+        self.assertTrue(now.timetuple() == now.utctimetuple())
+
+    def testUnknownOffsets(self):
+        # This tzinfo behavior is required to make
+        # datetime.time.{utcoffset, dst, tzname} work as documented.
+
+        dst_tz = pytz.timezone('US/Eastern')
+
+        # This information is not known when we don't have a date,
+        # so return None per API.
+        self.assertTrue(dst_tz.utcoffset(None) is None)
+        self.assertTrue(dst_tz.dst(None) is None)
+        # We don't know the abbreviation, but this is still a valid
+        # tzname per the Python documentation.
+        self.assertEqual(dst_tz.tzname(None), 'US/Eastern')
+
+    def clearCache(self):
+        pytz._tzinfo_cache.clear()
+
+    def testUnicodeTimezone(self):
+        # We need to ensure that cold lookups work for both Unicode
+        # and traditional strings, and that the desired singleton is
+        # returned.
+        self.clearCache()
+        eastern = pytz.timezone(unicode('US/Eastern'))
+        self.assertTrue(eastern is pytz.timezone('US/Eastern'))
+
+        self.clearCache()
+        eastern = pytz.timezone('US/Eastern')
+        self.assertTrue(eastern is pytz.timezone(unicode('US/Eastern')))
+
+    def testStaticTzInfo(self):
+        # Ensure that static timezones are correctly detected,
+        # per lp:1602807
+        static = pytz.timezone('Etc/GMT-4')
+        self.assertTrue(isinstance(static, StaticTzInfo))
+
+
+class PicklingTest(unittest.TestCase):
+
+    def _roundtrip_tzinfo(self, tz):
+        p = pickle.dumps(tz)
+        unpickled_tz = pickle.loads(p)
+        self.assertTrue(tz is unpickled_tz, '%s did not roundtrip' % tz.zone)
+
+    def _roundtrip_datetime(self, dt):
+        # Ensure that the tzinfo attached to a datetime instance
+        # is identical to the one returned. This is important for
+        # DST timezones, as some state is stored in the tzinfo.
+        tz = dt.tzinfo
+        p = pickle.dumps(dt)
+        unpickled_dt = pickle.loads(p)
+        unpickled_tz = unpickled_dt.tzinfo
+        self.assertTrue(tz is unpickled_tz, '%s did not roundtrip' % tz.zone)
+
+    def testDst(self):
+        tz = pytz.timezone('Europe/Amsterdam')
+        dt = datetime(2004, 2, 1, 0, 0, 0)
+
+        for localized_tz in tz._tzinfos.values():
+            self._roundtrip_tzinfo(localized_tz)
+            self._roundtrip_datetime(dt.replace(tzinfo=localized_tz))
+
+    def testRoundtrip(self):
+        dt = datetime(2004, 2, 1, 0, 0, 0)
+        for zone in pytz.all_timezones:
+            tz = pytz.timezone(zone)
+            self._roundtrip_tzinfo(tz)
+
+    def testDatabaseFixes(self):
+        # Hack the pickle to make it refer to a timezone abbreviation
+        # that does not match anything. The unpickler should be able
+        # to repair this case
+        tz = pytz.timezone('Australia/Melbourne')
+        p = pickle.dumps(tz)
+        tzname = tz._tzname
+        hacked_p = p.replace(_byte_string(tzname),
+                             _byte_string('?'*len(tzname)))
+        self.assertNotEqual(p, hacked_p)
+        unpickled_tz = pickle.loads(hacked_p)
+        self.assertTrue(tz is unpickled_tz)
+
+        # Simulate a database correction. In this case, the incorrect
+        # data will continue to be used.
+        p = pickle.dumps(tz)
+        new_utcoffset = tz._utcoffset.seconds + 42
+
+        # Python 3 introduced a new pickle protocol where numbers are stored in
+        # hexadecimal representation. Here we extract the pickle
+        # representation of the number for the current Python version.
+        old_pickle_pattern = pickle.dumps(tz._utcoffset.seconds)[3:-1]
+        new_pickle_pattern = pickle.dumps(new_utcoffset)[3:-1]
+        hacked_p = p.replace(old_pickle_pattern, new_pickle_pattern)
+
+        self.assertNotEqual(p, hacked_p)
+        unpickled_tz = pickle.loads(hacked_p)
+        self.assertEqual(unpickled_tz._utcoffset.seconds, new_utcoffset)
+        self.assertTrue(tz is not unpickled_tz)
+
+    def testOldPickles(self):
+        # Ensure that applications serializing pytz instances as pickles
+        # have no troubles upgrading to a new pytz release. These pickles
+        # where created with pytz2006j
+        east1 = pickle.loads(_byte_string(
+            "cpytz\n_p\np1\n(S'US/Eastern'\np2\nI-18000\n"
+            "I0\nS'EST'\np3\ntRp4\n."
+            ))
+        east2 = pytz.timezone('US/Eastern').localize(
+            datetime(2006, 1, 1)).tzinfo
+        self.assertTrue(east1 is east2)
+
+        # Confirm changes in name munging between 2006j and 2007c cause
+        # no problems.
+        pap1 = pickle.loads(_byte_string(
+            "cpytz\n_p\np1\n(S'America/Port_minus_au_minus_Prince'"
+            "\np2\nI-17340\nI0\nS'PPMT'\np3\ntRp4\n."))
+        pap2 = pytz.timezone('America/Port-au-Prince').localize(
+            datetime(1910, 1, 1)).tzinfo
+        self.assertTrue(pap1 is pap2)
+
+        gmt1 = pickle.loads(_byte_string(
+            "cpytz\n_p\np1\n(S'Etc/GMT_plus_10'\np2\ntRp3\n."))
+        gmt2 = pytz.timezone('Etc/GMT+10')
+        self.assertTrue(gmt1 is gmt2)
+
+
+class USEasternDSTStartTestCase(unittest.TestCase):
+    tzinfo = pytz.timezone('US/Eastern')
+
+    # 24 hours before DST changeover
+    transition_time = datetime(2002, 4, 7, 7, 0, 0, tzinfo=UTC)
+
+    # Increase for 'flexible' DST transitions due to 1 minute granularity
+    # of Python's datetime library
+    instant = timedelta(seconds=1)
+
+    # before transition
+    before = {
+        'tzname': 'EST',
+        'utcoffset': timedelta(hours = -5),
+        'dst': timedelta(hours = 0),
+        }
+
+    # after transition
+    after = {
+        'tzname': 'EDT',
+        'utcoffset': timedelta(hours = -4),
+        'dst': timedelta(hours = 1),
+        }
+
+    def _test_tzname(self, utc_dt, wanted):
+        tzname = wanted['tzname']
+        dt = utc_dt.astimezone(self.tzinfo)
+        self.assertEqual(dt.tzname(), tzname,
+            'Expected %s as tzname for %s. Got %s' % (
+                tzname, str(utc_dt), dt.tzname()
+                )
+            )
+
+    def _test_utcoffset(self, utc_dt, wanted):
+        utcoffset = wanted['utcoffset']
+        dt = utc_dt.astimezone(self.tzinfo)
+        self.assertEqual(
+                dt.utcoffset(), wanted['utcoffset'],
+                'Expected %s as utcoffset for %s. Got %s' % (
+                    utcoffset, utc_dt, dt.utcoffset()
+                    )
+                )
+
+    def _test_dst(self, utc_dt, wanted):
+        dst = wanted['dst']
+        dt = utc_dt.astimezone(self.tzinfo)
+        self.assertEqual(dt.dst(),dst,
+            'Expected %s as dst for %s. Got %s' % (
+                dst, utc_dt, dt.dst()
+                )
+            )
+
+    def test_arithmetic(self):
+        utc_dt = self.transition_time
+
+        for days in range(-420, 720, 20):
+            delta = timedelta(days=days)
+
+            # Make sure we can get back where we started
+            dt = utc_dt.astimezone(self.tzinfo)
+            dt2 = dt + delta
+            dt2 = dt2 - delta
+            self.assertEqual(dt, dt2)
+
+            # Make sure arithmetic crossing DST boundaries ends
+            # up in the correct timezone after normalization
+            utc_plus_delta = (utc_dt + delta).astimezone(self.tzinfo)
+            local_plus_delta = self.tzinfo.normalize(dt + delta)
+            self.assertEqual(
+                    prettydt(utc_plus_delta),
+                    prettydt(local_plus_delta),
+                    'Incorrect result for delta==%d days.  Wanted %r. Got %r'%(
+                        days,
+                        prettydt(utc_plus_delta),
+                        prettydt(local_plus_delta),
+                        )
+                    )
+
+    def _test_all(self, utc_dt, wanted):
+        self._test_utcoffset(utc_dt, wanted)
+        self._test_tzname(utc_dt, wanted)
+        self._test_dst(utc_dt, wanted)
+
+    def testDayBefore(self):
+        self._test_all(
+                self.transition_time - timedelta(days=1), self.before
+                )
+
+    def testTwoHoursBefore(self):
+        self._test_all(
+                self.transition_time - timedelta(hours=2), self.before
+                )
+
+    def testHourBefore(self):
+        self._test_all(
+                self.transition_time - timedelta(hours=1), self.before
+                )
+
+    def testInstantBefore(self):
+        self._test_all(
+                self.transition_time - self.instant, self.before
+                )
+
+    def testTransition(self):
+        self._test_all(
+                self.transition_time, self.after
+                )
+
+    def testInstantAfter(self):
+        self._test_all(
+                self.transition_time + self.instant, self.after
+                )
+
+    def testHourAfter(self):
+        self._test_all(
+                self.transition_time + timedelta(hours=1), self.after
+                )
+
+    def testTwoHoursAfter(self):
+        self._test_all(
+                self.transition_time + timedelta(hours=1), self.after
+                )
+
+    def testDayAfter(self):
+        self._test_all(
+                self.transition_time + timedelta(days=1), self.after
+                )
+
+
+class USEasternDSTEndTestCase(USEasternDSTStartTestCase):
+    tzinfo = pytz.timezone('US/Eastern')
+    transition_time = datetime(2002, 10, 27, 6, 0, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'EDT',
+        'utcoffset': timedelta(hours = -4),
+        'dst': timedelta(hours = 1),
+        }
+    after = {
+        'tzname': 'EST',
+        'utcoffset': timedelta(hours = -5),
+        'dst': timedelta(hours = 0),
+        }
+
+
+class USEasternEPTStartTestCase(USEasternDSTStartTestCase):
+    transition_time = datetime(1945, 8, 14, 23, 0, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'EWT',
+        'utcoffset': timedelta(hours = -4),
+        'dst': timedelta(hours = 1),
+        }
+    after = {
+        'tzname': 'EPT',
+        'utcoffset': timedelta(hours = -4),
+        'dst': timedelta(hours = 1),
+        }
+
+
+class USEasternEPTEndTestCase(USEasternDSTStartTestCase):
+    transition_time = datetime(1945, 9, 30, 6, 0, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'EPT',
+        'utcoffset': timedelta(hours = -4),
+        'dst': timedelta(hours = 1),
+        }
+    after = {
+        'tzname': 'EST',
+        'utcoffset': timedelta(hours = -5),
+        'dst': timedelta(hours = 0),
+        }
+
+
+class WarsawWMTEndTestCase(USEasternDSTStartTestCase):
+    # In 1915, Warsaw changed from Warsaw to Central European time.
+    # This involved the clocks being set backwards, causing a end-of-DST
+    # like situation without DST being involved.
+    tzinfo = pytz.timezone('Europe/Warsaw')
+    transition_time = datetime(1915, 8, 4, 22, 36, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'WMT',
+        'utcoffset': timedelta(hours=1, minutes=24),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'CET',
+        'utcoffset': timedelta(hours=1),
+        'dst': timedelta(0),
+        }
+
+
+class VilniusWMTEndTestCase(USEasternDSTStartTestCase):
+    # At the end of 1916, Vilnius changed timezones putting its clock
+    # forward by 11 minutes 35 seconds. Neither timezone was in DST mode.
+    tzinfo = pytz.timezone('Europe/Vilnius')
+    instant = timedelta(seconds=31)
+    transition_time = datetime(1916, 12, 31, 22, 36, 00, tzinfo=UTC)
+    before = {
+        'tzname': 'WMT',
+        'utcoffset': timedelta(hours=1, minutes=24),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'KMT',
+        'utcoffset': timedelta(hours=1, minutes=36), # Really 1:35:36
+        'dst': timedelta(0),
+        }
+
+
+class VilniusCESTStartTestCase(USEasternDSTStartTestCase):
+    # In 1941, Vilnius changed from MSG to CEST, switching to summer
+    # time while simultaneously reducing its UTC offset by two hours,
+    # causing the clocks to go backwards for this summer time
+    # switchover.
+    tzinfo = pytz.timezone('Europe/Vilnius')
+    transition_time = datetime(1941, 6, 23, 21, 00, 00, tzinfo=UTC)
+    before = {
+        'tzname': 'MSK',
+        'utcoffset': timedelta(hours=3),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'CEST',
+        'utcoffset': timedelta(hours=2),
+        'dst': timedelta(hours=1),
+        }
+
+
+class LondonHistoryStartTestCase(USEasternDSTStartTestCase):
+    # The first known timezone transition in London was in 1847 when
+    # clocks where synchronized to GMT. However, we currently only
+    # understand v1 format tzfile(5) files which does handle years
+    # this far in the past, so our earliest known transition is in
+    # 1916.
+    tzinfo = pytz.timezone('Europe/London')
+    # transition_time = datetime(1847, 12, 1, 1, 15, 00, tzinfo=UTC)
+    # before = {
+    #     'tzname': 'LMT',
+    #     'utcoffset': timedelta(minutes=-75),
+    #     'dst': timedelta(0),
+    #     }
+    # after = {
+    #     'tzname': 'GMT',
+    #     'utcoffset': timedelta(0),
+    #     'dst': timedelta(0),
+    #     }
+    transition_time = datetime(1916, 5, 21, 2, 00, 00, tzinfo=UTC)
+    before = {
+        'tzname': 'GMT',
+        'utcoffset': timedelta(0),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'BST',
+        'utcoffset': timedelta(hours=1),
+        'dst': timedelta(hours=1),
+        }
+
+
+class LondonHistoryEndTestCase(USEasternDSTStartTestCase):
+    # Timezone switchovers are projected into the future, even
+    # though no official statements exist or could be believed even
+    # if they did exist. We currently only check the last known
+    # transition in 2037, as we are still using v1 format tzfile(5)
+    # files.
+    tzinfo = pytz.timezone('Europe/London')
+    # transition_time = datetime(2499, 10, 25, 1, 0, 0, tzinfo=UTC)
+    transition_time = datetime(2037, 10, 25, 1, 0, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'BST',
+        'utcoffset': timedelta(hours=1),
+        'dst': timedelta(hours=1),
+        }
+    after = {
+        'tzname': 'GMT',
+        'utcoffset': timedelta(0),
+        'dst': timedelta(0),
+        }
+
+
+class NoumeaHistoryStartTestCase(USEasternDSTStartTestCase):
+    # Noumea adopted a whole hour offset in 1912. Previously
+    # it was 11 hours, 5 minutes and 48 seconds off UTC. However,
+    # due to limitations of the Python datetime library, we need
+    # to round that to 11 hours 6 minutes.
+    tzinfo = pytz.timezone('Pacific/Noumea')
+    transition_time = datetime(1912, 1, 12, 12, 54, 12, tzinfo=UTC)
+    before = {
+        'tzname': 'LMT',
+        'utcoffset': timedelta(hours=11, minutes=6),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'NCT',
+        'utcoffset': timedelta(hours=11),
+        'dst': timedelta(0),
+        }
+
+
+class NoumeaDSTEndTestCase(USEasternDSTStartTestCase):
+    # Noumea dropped DST in 1997.
+    tzinfo = pytz.timezone('Pacific/Noumea')
+    transition_time = datetime(1997, 3, 1, 15, 00, 00, tzinfo=UTC)
+    before = {
+        'tzname': 'NCST',
+        'utcoffset': timedelta(hours=12),
+        'dst': timedelta(hours=1),
+        }
+    after = {
+        'tzname': 'NCT',
+        'utcoffset': timedelta(hours=11),
+        'dst': timedelta(0),
+        }
+
+
+class NoumeaNoMoreDSTTestCase(NoumeaDSTEndTestCase):
+    # Noumea dropped DST in 1997. Here we test that it stops occuring.
+    transition_time = (
+        NoumeaDSTEndTestCase.transition_time + timedelta(days=365*10))
+    before = NoumeaDSTEndTestCase.after
+    after = NoumeaDSTEndTestCase.after
+
+
+class TahitiTestCase(USEasternDSTStartTestCase):
+    # Tahiti has had a single transition in its history.
+    tzinfo = pytz.timezone('Pacific/Tahiti')
+    transition_time = datetime(1912, 10, 1, 9, 58, 16, tzinfo=UTC)
+    before = {
+        'tzname': 'LMT',
+        'utcoffset': timedelta(hours=-9, minutes=-58),
+        'dst': timedelta(0),
+        }
+    after = {
+        'tzname': 'TAHT',
+        'utcoffset': timedelta(hours=-10),
+        'dst': timedelta(0),
+        }
+
+
+class SamoaInternationalDateLineChange(USEasternDSTStartTestCase):
+    # At the end of 2011, Samoa will switch from being east of the
+    # international dateline to the west. There will be no Dec 30th
+    # 2011 and it will switch from UTC-10 to UTC+14.
+    tzinfo = pytz.timezone('Pacific/Apia')
+    transition_time = datetime(2011, 12, 30, 10, 0, 0, tzinfo=UTC)
+    before = {
+        'tzname': 'SDT',
+        'utcoffset': timedelta(hours=-10),
+        'dst': timedelta(hours=1),
+        }
+    after = {
+        'tzname': 'WSDT',
+        'utcoffset': timedelta(hours=14),
+        'dst': timedelta(hours=1),
+        }
+
+
+class ReferenceUSEasternDSTStartTestCase(USEasternDSTStartTestCase):
+    tzinfo = reference.Eastern
+    def test_arithmetic(self):
+        # Reference implementation cannot handle this
+        pass
+
+
+class ReferenceUSEasternDSTEndTestCase(USEasternDSTEndTestCase):
+    tzinfo = reference.Eastern
+
+    def testHourBefore(self):
+        # Python's datetime library has a bug, where the hour before
+        # a daylight saving transition is one hour out. For example,
+        # at the end of US/Eastern daylight saving time, 01:00 EST
+        # occurs twice (once at 05:00 UTC and once at 06:00 UTC),
+        # whereas the first should actually be 01:00 EDT.
+        # Note that this bug is by design - by accepting this ambiguity
+        # for one hour one hour per year, an is_dst flag on datetime.time
+        # became unnecessary.
+        self._test_all(
+                self.transition_time - timedelta(hours=1), self.after
+                )
+
+    def testInstantBefore(self):
+        self._test_all(
+                self.transition_time - timedelta(seconds=1), self.after
+                )
+
+    def test_arithmetic(self):
+        # Reference implementation cannot handle this
+        pass
+
+
+class LocalTestCase(unittest.TestCase):
+    def testLocalize(self):
+        loc_tz = pytz.timezone('Europe/Amsterdam')
+
+        loc_time = loc_tz.localize(datetime(1930, 5, 10, 0, 0, 0))
+        # Actually +00:19:32, but Python datetime rounds this
+        self.assertEqual(loc_time.strftime('%Z%z'), 'AMT+0020')
+
+        loc_time = loc_tz.localize(datetime(1930, 5, 20, 0, 0, 0))
+        # Actually +00:19:32, but Python datetime rounds this
+        self.assertEqual(loc_time.strftime('%Z%z'), 'NST+0120')
+
+        loc_time = loc_tz.localize(datetime(1940, 5, 10, 0, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'NET+0020')
+
+        loc_time = loc_tz.localize(datetime(1940, 5, 20, 0, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'CEST+0200')
+
+        loc_time = loc_tz.localize(datetime(2004, 2, 1, 0, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'CET+0100')
+
+        loc_time = loc_tz.localize(datetime(2004, 4, 1, 0, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'CEST+0200')
+
+        tz = pytz.timezone('Europe/Amsterdam')
+        loc_time = loc_tz.localize(datetime(1943, 3, 29, 1, 59, 59))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'CET+0100')
+
+
+        # Switch to US
+        loc_tz = pytz.timezone('US/Eastern')
+
+        # End of DST ambiguity check
+        loc_time = loc_tz.localize(datetime(1918, 10, 27, 1, 59, 59), is_dst=1)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EDT-0400')
+
+        loc_time = loc_tz.localize(datetime(1918, 10, 27, 1, 59, 59), is_dst=0)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EST-0500')
+
+        self.assertRaises(pytz.AmbiguousTimeError,
+            loc_tz.localize, datetime(1918, 10, 27, 1, 59, 59), is_dst=None
+            )
+
+        # Start of DST non-existent times
+        loc_time = loc_tz.localize(datetime(1918, 3, 31, 2, 0, 0), is_dst=0)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EST-0500')
+
+        loc_time = loc_tz.localize(datetime(1918, 3, 31, 2, 0, 0), is_dst=1)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EDT-0400')
+
+        self.assertRaises(pytz.NonExistentTimeError,
+            loc_tz.localize, datetime(1918, 3, 31, 2, 0, 0), is_dst=None
+            )
+
+        # Weird changes - war time and peace time both is_dst==True
+
+        loc_time = loc_tz.localize(datetime(1942, 2, 9, 3, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EWT-0400')
+
+        loc_time = loc_tz.localize(datetime(1945, 8, 14, 19, 0, 0))
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EPT-0400')
+
+        loc_time = loc_tz.localize(datetime(1945, 9, 30, 1, 0, 0), is_dst=1)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EPT-0400')
+
+        loc_time = loc_tz.localize(datetime(1945, 9, 30, 1, 0, 0), is_dst=0)
+        self.assertEqual(loc_time.strftime('%Z%z'), 'EST-0500')
+
+        # Weird changes - ambiguous time (end-of-DST like) but is_dst==False
+        for zonename, ambiguous_naive, expected in [
+                ('Europe/Warsaw', datetime(1915, 8, 4, 23, 59, 59),
+                 ['1915-08-04 23:59:59 WMT+0124',
+                  '1915-08-04 23:59:59 CET+0100']),
+                ('Europe/Moscow', datetime(2014, 10, 26, 1, 30),
+                 ['2014-10-26 01:30:00 MSK+0400',
+                  '2014-10-26 01:30:00 MSK+0300'])]:
+            loc_tz = pytz.timezone(zonename)
+            self.assertRaises(pytz.AmbiguousTimeError,
+                loc_tz.localize, ambiguous_naive, is_dst=None
+                )
+            # Also test non-boolean is_dst in the weird case
+            for dst in [True, timedelta(1), False, timedelta(0)]:
+                loc_time = loc_tz.localize(ambiguous_naive, is_dst=dst)
+                self.assertEqual(loc_time.strftime(fmt), expected[not dst])
+
+    def testNormalize(self):
+        tz = pytz.timezone('US/Eastern')
+        dt = datetime(2004, 4, 4, 7, 0, 0, tzinfo=UTC).astimezone(tz)
+        dt2 = dt - timedelta(minutes=10)
+        self.assertEqual(
+                dt2.strftime('%Y-%m-%d %H:%M:%S %Z%z'),
+                '2004-04-04 02:50:00 EDT-0400'
+                )
+
+        dt2 = tz.normalize(dt2)
+        self.assertEqual(
+                dt2.strftime('%Y-%m-%d %H:%M:%S %Z%z'),
+                '2004-04-04 01:50:00 EST-0500'
+                )
+
+    def testPartialMinuteOffsets(self):
+        # utcoffset in Amsterdam was not a whole minute until 1937
+        # However, we fudge this by rounding them, as the Python
+        # datetime library
+        tz = pytz.timezone('Europe/Amsterdam')
+        utc_dt = datetime(1914, 1, 1, 13, 40, 28, tzinfo=UTC) # correct
+        utc_dt = utc_dt.replace(second=0) # But we need to fudge it
+        loc_dt = utc_dt.astimezone(tz)
+        self.assertEqual(
+                loc_dt.strftime('%Y-%m-%d %H:%M:%S %Z%z'),
+                '1914-01-01 14:00:00 AMT+0020'
+                )
+
+        # And get back...
+        utc_dt = loc_dt.astimezone(UTC)
+        self.assertEqual(
+                utc_dt.strftime('%Y-%m-%d %H:%M:%S %Z%z'),
+                '1914-01-01 13:40:00 UTC+0000'
+                )
+
+    def no_testCreateLocaltime(self):
+        # It would be nice if this worked, but it doesn't.
+        tz = pytz.timezone('Europe/Amsterdam')
+        dt = datetime(2004, 10, 31, 2, 0, 0, tzinfo=tz)
+        self.assertEqual(
+                dt.strftime(fmt),
+                '2004-10-31 02:00:00 CET+0100'
+                )
+
+
+class CommonTimezonesTestCase(unittest.TestCase):
+    def test_bratislava(self):
+        # Bratislava is the default timezone for Slovakia, but our
+        # heuristics where not adding it to common_timezones. Ideally,
+        # common_timezones should be populated from zone.tab at runtime,
+        # but I'm hesitant to pay the startup cost as loading the list
+        # on demand whilst remaining backwards compatible seems
+        # difficult.
+        self.assertTrue('Europe/Bratislava' in pytz.common_timezones)
+        self.assertTrue('Europe/Bratislava' in pytz.common_timezones_set)
+
+    def test_us_eastern(self):
+        self.assertTrue('US/Eastern' in pytz.common_timezones)
+        self.assertTrue('US/Eastern' in pytz.common_timezones_set)
+
+    def test_belfast(self):
+        # Belfast uses London time.
+        self.assertTrue('Europe/Belfast' in pytz.all_timezones_set)
+        self.assertFalse('Europe/Belfast' in pytz.common_timezones)
+        self.assertFalse('Europe/Belfast' in pytz.common_timezones_set)
+
+
+class BaseTzInfoTestCase:
+    '''Ensure UTC, StaticTzInfo and DstTzInfo work consistently.
+
+    These tests are run for each type of tzinfo.
+    '''
+    tz = None  # override
+    tz_class = None  # override
+
+    def test_expectedclass(self):
+        self.assertTrue(isinstance(self.tz, self.tz_class))
+
+    def test_fromutc(self):
+        # naive datetime.
+        dt1 = datetime(2011, 10, 31)
+
+        # localized datetime, same timezone.
+        dt2 = self.tz.localize(dt1)
+
+        # Both should give the same results. Note that the standard
+        # Python tzinfo.fromutc() only supports the second.
+        for dt in [dt1, dt2]:
+            loc_dt = self.tz.fromutc(dt)
+            loc_dt2 = pytz.utc.localize(dt1).astimezone(self.tz)
+            self.assertEqual(loc_dt, loc_dt2)
+
+        # localized datetime, different timezone.
+        new_tz = pytz.timezone('Europe/Paris')
+        self.assertTrue(self.tz is not new_tz)
+        dt3 = new_tz.localize(dt1)
+        self.assertRaises(ValueError, self.tz.fromutc, dt3)
+
+    def test_normalize(self):
+        other_tz = pytz.timezone('Europe/Paris')
+        self.assertTrue(self.tz is not other_tz)
+
+        dt = datetime(2012, 3, 26, 12, 0)
+        other_dt = other_tz.localize(dt)
+
+        local_dt = self.tz.normalize(other_dt)
+
+        self.assertTrue(local_dt.tzinfo is not other_dt.tzinfo)
+        self.assertNotEqual(
+            local_dt.replace(tzinfo=None), other_dt.replace(tzinfo=None))
+
+    def test_astimezone(self):
+        other_tz = pytz.timezone('Europe/Paris')
+        self.assertTrue(self.tz is not other_tz)
+
+        dt = datetime(2012, 3, 26, 12, 0)
+        other_dt = other_tz.localize(dt)
+
+        local_dt = other_dt.astimezone(self.tz)
+
+        self.assertTrue(local_dt.tzinfo is not other_dt.tzinfo)
+        self.assertNotEqual(
+            local_dt.replace(tzinfo=None), other_dt.replace(tzinfo=None))
+
+
+class OptimizedUTCTestCase(unittest.TestCase, BaseTzInfoTestCase):
+    tz = pytz.utc
+    tz_class = tz.__class__
+
+
+class LegacyUTCTestCase(unittest.TestCase, BaseTzInfoTestCase):
+    # Deprecated timezone, but useful for comparison tests.
+    tz = pytz.timezone('Etc/UTC')
+    tz_class = StaticTzInfo
+
+
+class StaticTzInfoTestCase(unittest.TestCase, BaseTzInfoTestCase):
+    tz = pytz.timezone('GMT')
+    tz_class = StaticTzInfo
+
+
+class DstTzInfoTestCase(unittest.TestCase, BaseTzInfoTestCase):
+    tz = pytz.timezone('Australia/Melbourne')
+    tz_class = DstTzInfo
+
+
+def test_suite():
+    suite = unittest.TestSuite()
+    suite.addTest(doctest.DocTestSuite('pytz'))
+    suite.addTest(doctest.DocTestSuite('pytz.tzinfo'))
+    import test_tzinfo
+    suite.addTest(unittest.defaultTestLoader.loadTestsFromModule(test_tzinfo))
+    return suite
+
+
+if __name__ == '__main__':
+    warnings.simplefilter("error") # Warnings should be fatal in tests.
+    unittest.main(defaultTest='test_suite')

lib/pytz/tzfile.py

@@ -0,0 +1,137 @@
+#!/usr/bin/env python
+'''
+$Id: tzfile.py,v 1.8 2004/06/03 00:15:24 zenzen Exp $
+'''
+
+try:
+    from cStringIO import StringIO
+except ImportError:
+    from io import StringIO
+from datetime import datetime, timedelta
+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)
+    #print tz.asPython(4)
+    #print tz.transitions_mapping

lib/pytz/tzinfo.py

@@ -0,0 +1,564 @@
+'''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.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.utcfromtimestamp(seconds) 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
+    _utc_transition_times = None # Sorted list of DST transition times in UTC
+    _transition_info = None # [(utcoffset, dstoffset, tzname)] corresponding
+                            # to _utc_transition_times entries
+    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 occuring 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)
+
+        >>> tz.utcoffset(ambiguous, is_dst=False)
+        datetime.timedelta(-1, 73800)
+
+        >>> tz.utcoffset(ambiguous, is_dst=True)
+        datetime.timedelta(-1, 77400)
+
+        >>> 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)
+
+        >>> tz.dst(normal)
+        datetime.timedelta(0, 3600)
+        >>> tz.dst(normal, is_dst=False)
+        datetime.timedelta(0, 3600)
+        >>> tz.dst(normal, is_dst=True)
+        datetime.timedelta(0, 3600)
+
+        >>> ambiguous = datetime(2009, 10, 31, 23, 30)
+
+        >>> tz.dst(ambiguous, is_dst=False)
+        datetime.timedelta(0)
+        >>> tz.dst(ambiguous, is_dst=True)
+        datetime.timedelta(0, 3600)
+        >>> 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]