win32timezone.py

# -*- coding: UTF-8 -*-

"""
win32timezone:
	Module for handling datetime.tzinfo time zones using the windows
registry for time zone information.  The time zone names are dependent
on the registry entries defined by the operating system.

	This module may be tested using the doctest module.

	Written by Jason R. Coombs (jaraco@jaraco.com).
	Copyright © 2003-2012.
	All Rights Reserved.

	This module is licenced for use in Mark Hammond's pywin32
library under the same terms as the pywin32 library.

	To use this time zone module with the datetime module, simply pass
the TimeZoneInfo object to the datetime constructor.  For example,

>>> import win32timezone, datetime
>>> assert 'Mountain Standard Time' in win32timezone.TimeZoneInfo.get_sorted_time_zone_names()
>>> MST = win32timezone.TimeZoneInfo('Mountain Standard Time')
>>> now = datetime.datetime.now(MST)

	The now object is now a time-zone aware object, and daylight savings-
aware methods may be called on it.

>>> now.utcoffset() in (datetime.timedelta(-1, 61200), datetime.timedelta(-1, 64800))
True

(note that the result of utcoffset call will be different based on when now was
generated, unless standard time is always used)

>>> now = datetime.datetime.now(TimeZoneInfo('Mountain Standard Time', True))
>>> now.utcoffset()
datetime.timedelta(-1, 61200)

>>> aug2 = datetime.datetime(2003, 8, 2, tzinfo = MST)
>>> tuple(aug2.utctimetuple())
(2003, 8, 2, 6, 0, 0, 5, 214, 0)
>>> nov2 = datetime.datetime(2003, 11, 25, tzinfo = MST)
>>> tuple(nov2.utctimetuple())
(2003, 11, 25, 7, 0, 0, 1, 329, 0)

To convert from one timezone to another, just use the astimezone method.

>>> aug2.isoformat()
'2003-08-02T00:00:00-06:00'
>>> aug2est = aug2.astimezone(win32timezone.TimeZoneInfo('Eastern Standard Time'))
>>> aug2est.isoformat()
'2003-08-02T02:00:00-04:00'

calling the displayName member will return the display name as set in the
registry.

>>> est = win32timezone.TimeZoneInfo('Eastern Standard Time')
>>> str(est.displayName)
'(UTC-05:00) Eastern Time (US & Canada)'

>>> gmt = win32timezone.TimeZoneInfo('GMT Standard Time', True)
>>> str(gmt.displayName)
'(UTC) Dublin, Edinburgh, Lisbon, London'

To get the complete list of available time zone keys,
>>> zones = win32timezone.TimeZoneInfo.get_all_time_zones()

If you want to get them in an order that's sorted longitudinally
>>> zones = win32timezone.TimeZoneInfo.get_sorted_time_zones()

TimeZoneInfo now supports being pickled and comparison
>>> import pickle
>>> tz = win32timezone.TimeZoneInfo('China Standard Time')
>>> tz == pickle.loads(pickle.dumps(tz))
True

It's possible to construct a TimeZoneInfo from a TimeZoneDescription
including the currently-defined zone.
>>> tz = win32timezone.TimeZoneInfo(TimeZoneDefinition.current())
>>> tz == pickle.loads(pickle.dumps(tz))
True

>>> aest = win32timezone.TimeZoneInfo('AUS Eastern Standard Time')
>>> est = win32timezone.TimeZoneInfo('E. Australia Standard Time')
>>> dt = datetime.datetime(2006, 11, 11, 1, 0, 0, tzinfo = aest)
>>> estdt = dt.astimezone(est)
>>> estdt.strftime('%Y-%m-%d %H:%M:%S')
'2006-11-11 00:00:00'

>>> dt = datetime.datetime(2007, 1, 12, 1, 0, 0, tzinfo = aest)
>>> estdt = dt.astimezone(est)
>>> estdt.strftime('%Y-%m-%d %H:%M:%S')
'2007-01-12 00:00:00'

>>> dt = datetime.datetime(2007, 6, 13, 1, 0, 0, tzinfo = aest)
>>> estdt = dt.astimezone(est)
>>> estdt.strftime('%Y-%m-%d %H:%M:%S')
'2007-06-13 01:00:00'

Microsoft now has a patch for handling time zones in 2007 (see
http://support.microsoft.com/gp/cp_dst)

As a result, patched systems will give an incorrect result for
dates prior to the designated year except for Vista and its
successors, which have dynamic time zone support.
>>> nov2_pre_change = datetime.datetime(2003, 11, 2, tzinfo = MST)
>>> old_response = (2003, 11, 2, 7, 0, 0, 6, 306, 0)
>>> incorrect_patch_response = (2003, 11, 2, 6, 0, 0, 6, 306, 0)
>>> pre_response = nov2_pre_change.utctimetuple()
>>> pre_response in (old_response, incorrect_patch_response)
True

Furthermore, unpatched systems pre-Vista will give an incorrect
result for dates after 2007.
>>> nov2_post_change = datetime.datetime(2007, 11, 2, tzinfo = MST)
>>> incorrect_unpatched_response = (2007, 11, 2, 7, 0, 0, 4, 306, 0)
>>> new_response = (2007, 11, 2, 6, 0, 0, 4, 306, 0)
>>> post_response = nov2_post_change.utctimetuple()
>>> post_response in (new_response, incorrect_unpatched_response)
True


There is a function you can call to get some capabilities of the time
zone data.
>>> caps = GetTZCapabilities()
>>> isinstance(caps, dict)
True
>>> 'MissingTZPatch' in caps
True
>>> 'DynamicTZSupport' in caps
True

>>> both_dates_correct = (pre_response == old_response and post_response == new_response)
>>> old_dates_wrong = (pre_response == incorrect_patch_response)
>>> new_dates_wrong = (post_response == incorrect_unpatched_response)

>>> caps['DynamicTZSupport'] == both_dates_correct
True

>>> (not caps['DynamicTZSupport'] and caps['MissingTZPatch']) == new_dates_wrong
True

>>> (not caps['DynamicTZSupport'] and not caps['MissingTZPatch']) == old_dates_wrong
True

This test helps ensure language support for unicode characters
>>> x = TIME_ZONE_INFORMATION(0, u'français')


Test conversion from one time zone to another at a DST boundary
===============================================================

>>> tz_hi = TimeZoneInfo('Hawaiian Standard Time')
>>> tz_pac = TimeZoneInfo('Pacific Standard Time')
>>> time_before = datetime.datetime(2011, 11, 5, 15, 59, 59, tzinfo=tz_hi)
>>> tz_hi.utcoffset(time_before)
datetime.timedelta(-1, 50400)
>>> tz_hi.dst(time_before)
datetime.timedelta(0)

Hawaii doesn't need dynamic TZ info
>>> getattr(tz_hi, 'dynamicInfo', None)

Here's a time that gave some trouble as reported in #3523104
because one minute later, the equivalent UTC time changes from DST
in the U.S.
>>> dt_hi = datetime.datetime(2011, 11, 5, 15, 59, 59, 0, tzinfo=tz_hi)
>>> dt_hi.timetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=5, tm_hour=15, tm_min=59, tm_sec=59, tm_wday=5, tm_yday=309, tm_isdst=0)
>>> dt_hi.utctimetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=6, tm_hour=1, tm_min=59, tm_sec=59, tm_wday=6, tm_yday=310, tm_isdst=0)

Convert the time to pacific time.
>>> dt_pac = dt_hi.astimezone(tz_pac)
>>> dt_pac.timetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=5, tm_hour=18, tm_min=59, tm_sec=59, tm_wday=5, tm_yday=309, tm_isdst=1)

Notice that the UTC time is almost 2am.
>>> dt_pac.utctimetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=6, tm_hour=1, tm_min=59, tm_sec=59, tm_wday=6, tm_yday=310, tm_isdst=0)

Now do the same tests one minute later in Hawaii.
>>> time_after = datetime.datetime(2011, 11, 5, 16, 0, 0, 0, tzinfo=tz_hi)
>>> tz_hi.utcoffset(time_after)
datetime.timedelta(-1, 50400)
>>> tz_hi.dst(time_before)
datetime.timedelta(0)

>>> dt_hi = datetime.datetime(2011, 11, 5, 16, 0, 0, 0, tzinfo=tz_hi)
>>> print dt_hi.timetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=5, tm_hour=16, tm_min=0, tm_sec=0, tm_wday=5, tm_yday=309, tm_isdst=0)
>>> print dt_hi.utctimetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=6, tm_hour=2, tm_min=0, tm_sec=0, tm_wday=6, tm_yday=310, tm_isdst=0)

According to the docs, this is what astimezone does.
>>> utc = (dt_hi - dt_hi.utcoffset()).replace(tzinfo=tz_pac)
>>> utc
datetime.datetime(2011, 11, 6, 2, 0, tzinfo=TimeZoneInfo('Pacific Standard Time'))
>>> tz_pac.fromutc(utc) == dt_hi.astimezone(tz_pac)
True
>>> tz_pac.fromutc(utc)
datetime.datetime(2011, 11, 5, 19, 0, tzinfo=TimeZoneInfo('Pacific Standard Time'))

Make sure the converted time is correct.
>>> dt_pac = dt_hi.astimezone(tz_pac)
>>> dt_pac.timetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=5, tm_hour=19, tm_min=0, tm_sec=0, tm_wday=5, tm_yday=309, tm_isdst=1)
>>> dt_pac.utctimetuple()
time.struct_time(tm_year=2011, tm_mon=11, tm_mday=6, tm_hour=2, tm_min=0, tm_sec=0, tm_wday=6, tm_yday=310, tm_isdst=0)

Check some internal methods
>>> tz_pac._getStandardBias(datetime.datetime(2011, 1, 1))
datetime.timedelta(0, 28800)
>>> tz_pac._getDaylightBias(datetime.datetime(2011, 1, 1))
datetime.timedelta(0, 25200)

Test the offsets
>>> offset = tz_pac.utcoffset(datetime.datetime(2011, 11, 6, 2, 0))
>>> offset == datetime.timedelta(hours=-8)
True
>>> dst_offset = tz_pac.dst(datetime.datetime(2011, 11, 6, 2, 0) + offset)
>>> dst_offset == datetime.timedelta(hours=1)
True
>>> (offset + dst_offset) == datetime.timedelta(hours=-7)
True


Test offsets that occur right at the DST changeover
>>> datetime.datetime.utcfromtimestamp(1320570000).replace(
...     tzinfo=TimeZoneInfo.utc()).astimezone(tz_pac)
datetime.datetime(2011, 11, 6, 1, 0, tzinfo=TimeZoneInfo('Pacific Standard Time'))

"""
from __future__ import generators

__author__ = 'Jason R. Coombs <jaraco@jaraco.com>'

import winreg
import struct
import datetime
import win32api
import re
import operator
import warnings
from itertools import count

import logging
log = logging.getLogger(__file__)

# A couple of objects for working with objects as if they were native C-type
# structures.
class _SimpleStruct(object):
	_fields_ = None # must be overridden by subclasses
	def __init__(self, *args, **kw):
		for i, (name, typ) in enumerate(self._fields_):
			def_arg = None
			if i < len(args):
				def_arg = args[i]
			if name in kw:
				def_arg = kw[name]
			if def_arg is not None:
				if not isinstance(def_arg, tuple):
					def_arg = (def_arg,)
			else:
				def_arg = ()
			if len(def_arg)==1 and isinstance(def_arg[0], typ):
				# already an object of this type.
				# XXX - should copy.copy???
				def_val = def_arg[0]
			else:
				def_val = typ(*def_arg)
			setattr(self, name, def_val)

	def field_names(self):
		return [f[0] for f in self._fields_]

	def __eq__(self, other):
		if not hasattr(other, "_fields_"):
			return False
		if self._fields_ != other._fields_:
			return False
		for name, _ in self._fields_:
			if getattr(self, name) != getattr(other, name):
				return False
		return True

	def __ne__(self, other):
		return not self.__eq__(other)

class SYSTEMTIME(_SimpleStruct):
	_fields_ = [
		('year', int),
		('month', int),
		('day_of_week', int),
		('day', int),
		('hour', int),
		('minute', int),
		('second', int),
		('millisecond', int),
	]

class TIME_ZONE_INFORMATION(_SimpleStruct):
	_fields_ = [
		('bias', int),
		('standard_name', str),
		('standard_start', SYSTEMTIME),
		('standard_bias', int),
		('daylight_name', str),
		('daylight_start', SYSTEMTIME),
		('daylight_bias', int),
	]

class DYNAMIC_TIME_ZONE_INFORMATION(_SimpleStruct):
	_fields_ = TIME_ZONE_INFORMATION._fields_ + [
		('key_name', str),
		('dynamic_daylight_time_disabled', bool),
	]


class TimeZoneDefinition(DYNAMIC_TIME_ZONE_INFORMATION):
	"""
	A time zone definition class based on the win32
	DYNAMIC_TIME_ZONE_INFORMATION structure.

	Describes a bias against UTC (bias), and two dates at which a separate
	additional bias applies (standard_bias and daylight_bias).
	"""

	def __init__(self, *args, **kwargs):
		"""
		Try to construct a TimeZoneDefinition from
		a) [DYNAMIC_]TIME_ZONE_INFORMATION args
		b) another TimeZoneDefinition
		c) a byte structure (using _from_bytes)
		"""
		try:
			super(TimeZoneDefinition, self).__init__(*args, **kwargs)
			return
		except (TypeError, ValueError):
			pass

		try:
			self.__init_from_other(*args, **kwargs)
			return
		except TypeError:
			pass

		try:
			self.__init_from_bytes(*args, **kwargs)
			return
		except TypeError:
			pass

		raise TypeError("Invalid arguments for %s" % self.__class__)

	def __init_from_bytes(self, bytes, standard_name='', daylight_name='', key_name='', daylight_disabled=False):
		format = '3l8h8h'
		components = struct.unpack(format, bytes)
		bias, standard_bias, daylight_bias = components[:3]
		standard_start = SYSTEMTIME(*components[3:11])
		daylight_start = SYSTEMTIME(*components[11:19])
		super(TimeZoneDefinition, self).__init__(bias,
			standard_name, standard_start, standard_bias,
			daylight_name, daylight_start, daylight_bias,
			key_name, daylight_disabled,)

	def __init_from_other(self, other):
		if not isinstance(other, TIME_ZONE_INFORMATION):
			raise TypeError("Not a TIME_ZONE_INFORMATION")
		for name in other.field_names():
			# explicitly get the value from the underlying structure
			value = super(TimeZoneDefinition, other).__getattribute__(other, name)
			setattr(self, name, value)
		# consider instead of the loop above just copying the memory directly
		#size = max(ctypes.sizeof(DYNAMIC_TIME_ZONE_INFO), ctypes.sizeof(other))
		#ctypes.memmove(ctypes.addressof(self), other, size)

	def __getattribute__(self, attr):
		value = super(TimeZoneDefinition, self).__getattribute__(attr)
		if 'bias' in attr:
			make_minute_timedelta = lambda m: datetime.timedelta(minutes = m)
			value = make_minute_timedelta(value)
		return value

	@classmethod
	def current(class_):
		"Windows Platform SDK GetTimeZoneInformation"
		code, tzi = win32api.GetTimeZoneInformation(True)
		return code, class_(*tzi)

	def set(self):
		tzi = tuple(getattr(self, n) for n, t in self._fields_)
		win32api.SetTimeZoneInformation(tzi)

	def copy(self):
		# XXX - this is no longer a copy!
		return self.__class__(self)

	def locate_daylight_start(self, year):
		return self._locate_day(year, self.daylight_start)

	def locate_standard_start(self, year):
		return self._locate_day(year, self.standard_start)

	@staticmethod
	def _locate_day(year, cutoff):
		"""
		Takes a SYSTEMTIME object, such as retrieved from a TIME_ZONE_INFORMATION
		structure or call to GetTimeZoneInformation and interprets it based on the given
		year to identify the actual day.

		This method is necessary because the SYSTEMTIME structure refers to a day by its
		day of the week and week of the month (e.g. 4th saturday in March).

		>>> SATURDAY = 6
		>>> MARCH = 3
		>>> st = SYSTEMTIME(2000, MARCH, SATURDAY, 4, 0, 0, 0, 0)

		# according to my calendar, the 4th Saturday in March in 2009 was the 28th
		>>> expected_date = datetime.datetime(2009, 3, 28)
		>>> TimeZoneDefinition._locate_day(2009, st) == expected_date
		True
		"""
		# MS stores Sunday as 0, Python datetime stores Monday as zero
		target_weekday = (cutoff.day_of_week + 6) % 7
		# For SYSTEMTIMEs relating to time zone inforamtion, cutoff.day
		#  is the week of the month
		week_of_month = cutoff.day
		# so the following is the first day of that week
		day = (week_of_month - 1) * 7 + 1
		result = datetime.datetime(year, cutoff.month, day,
			cutoff.hour, cutoff.minute, cutoff.second, cutoff.millisecond)
		# now the result is the correct week, but not necessarily the correct day of the week
		days_to_go = (target_weekday - result.weekday()) % 7
		result += datetime.timedelta(days_to_go)
		# if we selected a day in the month following the target month,
		#  move back a week or two.
		# This is necessary because Microsoft defines the fifth week in a month
		#  to be the last week in a month and adding the time delta might have
		#  pushed the result into the next month.
		while result.month == cutoff.month + 1:
			result -= datetime.timedelta(weeks = 1)
		return result

class TimeZoneInfo(datetime.tzinfo):
	"""
	Main class for handling Windows time zones.
	Usage:
		TimeZoneInfo(<Time Zone Standard Name>, [<Fix Standard Time>])

	If <Fix Standard Time> evaluates to True, daylight savings time is
	calculated in the same way as standard time.

	>>> tzi = TimeZoneInfo('Pacific Standard Time')
	>>> march31 = datetime.datetime(2000,3,31)

	We know that time zone definitions haven't changed from 2007
	to 2012, so regardless of whether dynamic info is available,
	there should be consistent results for these years.
	>>> subsequent_years = [march31.replace(year=year)
	...     for year in range(2007, 2013)]
	>>> offsets = set(tzi.utcoffset(year) for year in subsequent_years)
	>>> len(offsets)
	1
	"""

	# this key works for WinNT+, but not for the Win95 line.
	tzRegKey = r'SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones'

	def __init__(self, param=None, fix_standard_time=False):
		if isinstance(param, TimeZoneDefinition):
			self._LoadFromTZI(param)
		if isinstance(param, str):
			self.timeZoneName = param
			self._LoadInfoFromKey()
		self.fixedStandardTime = fix_standard_time

	def _FindTimeZoneKey(self):
		"""Find the registry key for the time zone name (self.timeZoneName)."""
		# for multi-language compatability, match the time zone name in the
		# "Std" key of the time zone key.
		zoneNames = dict(self._get_indexed_time_zone_keys('Std'))
		# Also match the time zone key name itself, to be compatible with
		# English-based hard-coded time zones.
		timeZoneName = zoneNames.get(self.timeZoneName, self.timeZoneName)
		key = _RegKeyDict.open(winreg.HKEY_LOCAL_MACHINE, self.tzRegKey)
		try:
			result = key.subkey(timeZoneName)
		except:
			raise ValueError('Timezone Name %s not found.' % timeZoneName)
		return result

	def _LoadInfoFromKey(self):
		"""Loads the information from an opened time zone registry key
		into relevant fields of this TZI object"""
		key = self._FindTimeZoneKey()
		self.displayName = key['Display']
		self.standardName = key['Std']
		self.daylightName = key['Dlt']
		self.staticInfo = TimeZoneDefinition(key['TZI'])
		self._LoadDynamicInfoFromKey(key)

	def _LoadFromTZI(self, tzi):
		self.timeZoneName = tzi.standard_name
		self.displayName = 'Unknown'
		self.standardName = tzi.standard_name
		self.daylightName = tzi.daylight_name
		self.staticInfo = tzi

	def _LoadDynamicInfoFromKey(self, key):
		"""
		>>> tzi = TimeZoneInfo('Central Standard Time')

		Here's how the RangeMap is supposed to work:
		>>> m = RangeMap(zip([2006,2007], 'BC'),
		...     sort_params = dict(reverse=True),
		...     key_match_comparator=operator.ge)
		>>> m.get(2000, 'A')
		'A'
		>>> m[2006]
		'B'
		>>> m[2007]
		'C'
		>>> m[2008]
		'C'

		>>> m[RangeMap.last_item]
		'B'

		>>> m.get(2008, m[RangeMap.last_item])
		'C'


		Now test the dynamic info (but fallback to our simple RangeMap
		on systems that don't have dynamicInfo).

		>>> dinfo = getattr(tzi, 'dynamicInfo', m)
		>>> 2007 in dinfo
		True
		>>> 2008 in dinfo
		False
		>>> dinfo[2007] == dinfo[2008] == dinfo[2012]
		True
		"""
		try:
			info = key.subkey('Dynamic DST')
		except WindowsError:
			return
		del info['FirstEntry']
		del info['LastEntry']
		years = map(int, list(info.keys()))
		values = map(TimeZoneDefinition, list(info.values()))
		# create a range mapping that searches by descending year and matches
		# if the target year is greater or equal.
		self.dynamicInfo = RangeMap(zip(years, values),
			sort_params = dict(reverse=True),
			key_match_comparator = operator.ge)

	def __repr__(self):
		result = '%s(%s' % (self.__class__.__name__, repr(self.timeZoneName))
		if self.fixedStandardTime:
			result += ', True'
		result += ')'
		return result

	def __str__(self):
		return self.displayName

	def tzname(self, dt):
		winInfo = self.getWinInfo(dt)
		if self.dst(dt) == winInfo.daylight_bias:
			result = self.daylightName
		elif self.dst(dt) == winInfo.standard_bias:
			result = self.standardName
		return result

	def getWinInfo(self, targetYear):
		"""
		Return the most relevant "info" for this time zone
		in the target year.
		"""
		if not hasattr(self, 'dynamicInfo') or not self.dynamicInfo:
			return self.staticInfo
		# Find the greatest year entry in self.dynamicInfo which is for
		#  a year greater than or equal to our targetYear. If not found,
		#  default to the earliest year.
		return self.dynamicInfo.get(targetYear,
			self.dynamicInfo[RangeMap.last_item])

	def _getStandardBias(self, dt):
		winInfo = self.getWinInfo(dt.year)
		return winInfo.bias + winInfo.standard_bias

	def _getDaylightBias(self, dt):
		winInfo = self.getWinInfo(dt.year)
		return winInfo.bias + winInfo.daylight_bias

	def utcoffset(self, dt):
		"Calculates the utcoffset according to the datetime.tzinfo spec"
		if dt is None: return
		winInfo = self.getWinInfo(dt.year)
		return -winInfo.bias + self.dst(dt)

	def dst(self, dt):
		"Calculates the daylight savings offset according to the datetime.tzinfo spec"
		if dt is None: return
		winInfo = self.getWinInfo(dt.year)
		if not self.fixedStandardTime and self._inDaylightSavings(dt):
			result = winInfo.daylight_bias
		else:
			result = winInfo.standard_bias
		return -result

	def _inDaylightSavings(self, dt):
		dt = dt.replace(tzinfo=None)
		winInfo = self.getWinInfo(dt.year)
		try:
			dstStart = self.GetDSTStartTime(dt.year)
			dstEnd = self.GetDSTEndTime(dt.year)

			# at the end of DST, when clocks are moved back, there's a period
			#  of daylight_bias where it's ambiguous whether we're in DST or
			#  not.
			dstEndAdj = dstEnd + winInfo.daylight_bias

			# the same thing could theoretically happen at the start of DST
			#  if there's a standard_bias (which I suspect is always 0).
			dstStartAdj = dstStart + winInfo.standard_bias

			if dstStart < dstEnd:
				in_dst = dstStartAdj <= dt < dstEndAdj
			else:
				# in the southern hemisphere, daylight savings time
				#  typically ends before it begins in a given year.
				in_dst = not (dstEndAdj < dt <= dstStartAdj)
		except ValueError:
			# there was an error parsing the time zone, which is normal when a
			#  start and end time are not specified.
			in_dst = False

		return in_dst

	def GetDSTStartTime(self, year):
		"Given a year, determines the time when daylight savings time starts"
		return self.getWinInfo(year).locate_daylight_start(year)

	def GetDSTEndTime(self, year):
		"Given a year, determines the time when daylight savings ends."
		return self.getWinInfo(year).locate_standard_start(year)

	def __cmp__(self, other):
		return cmp(self.__dict__, other.__dict__)

	def __eq__(self, other):
		return self.__dict__==other.__dict__

	def __ne__(self, other):
		return self.__dict__!=other.__dict__

	@classmethod
	def local(class_):
		"""Returns the local time zone as defined by the operating system in the
		registry.
		>>> localTZ = TimeZoneInfo.local()
		>>> now_local = datetime.datetime.now(localTZ)
		>>> now_UTC = datetime.datetime.utcnow()
		>>> (now_UTC - now_local) < datetime.timedelta(seconds = 5)
		Traceback (most recent call last):
		...
		TypeError: can't subtract offset-naive and offset-aware datetimes

		>>> now_UTC = now_UTC.replace(tzinfo = TimeZoneInfo('GMT Standard Time', True))

		Now one can compare the results of the two offset aware values
		>>> (now_UTC - now_local) < datetime.timedelta(seconds = 5)
		True
		"""
		code, info = TimeZoneDefinition.current()
		# code is 0 if daylight savings is disabled or not defined
		#  code is 1 or 2 if daylight savings is enabled, 2 if currently active
		fix_standard_time = not code
		# note that although the given information is sufficient to construct a WinTZI object, it's
		#  not sufficient to represent the time zone in which the current user is operating due
		#  to dynamic time zones.
		return class_(info, fix_standard_time)

	@classmethod
	def utc(class_):
		"""Returns a time-zone representing UTC.

		Same as TimeZoneInfo('GMT Standard Time', True) but caches the result
		for performance.

		>>> isinstance(TimeZoneInfo.utc(), TimeZoneInfo)
		True
		"""
		if not '_tzutc' in class_.__dict__:
			setattr(class_, '_tzutc', class_('GMT Standard Time', True))
		return class_._tzutc

	# helper methods for accessing the timezone info from the registry
	@staticmethod
	def _get_time_zone_key(subkey=None):
		"Return the registry key that stores time zone details"
		key = _RegKeyDict.open(winreg.HKEY_LOCAL_MACHINE, TimeZoneInfo.tzRegKey)
		if subkey:
			key = key.subkey(subkey)
		return key

	@staticmethod
	def _get_time_zone_key_names():
		"Returns the names of the (registry keys of the) time zones"
		return TimeZoneInfo._get_time_zone_key().subkeys()

	@staticmethod
	def _get_indexed_time_zone_keys(index_key='Index'):
		"""
		Get the names of the registry keys indexed by a value in that key.
		"""
		key_names = list(TimeZoneInfo._get_time_zone_key_names())
		def get_index_value(key_name):
			key = TimeZoneInfo._get_time_zone_key(key_name)
			return key[index_key]
		values = map(get_index_value, key_names)
		return zip(values, key_names)

	@staticmethod
	def get_sorted_time_zone_names():
		"Return a list of time zone names that can be used to initialize TimeZoneInfo instances"
		tzs = TimeZoneInfo.get_sorted_time_zones()
		get_standard_name = lambda tzi: tzi.standardName
		return [get_standard_name(tz) for tz in tzs]

	@staticmethod
	def get_all_time_zones():
		return [TimeZoneInfo(n) for n in TimeZoneInfo._get_time_zone_key_names()]

	@staticmethod
	def get_sorted_time_zones(key=None):
		"""
		Return the time zones sorted by some key.
		key must be a function that takes a TimeZoneInfo object and returns
		a value suitable for sorting on.
		The key defaults to the bias (descending), as is done in Windows
		(see http://blogs.msdn.com/michkap/archive/2006/12/22/1350684.aspx)
		"""
		key = key or (lambda tzi: -tzi.staticInfo.bias)
		zones = TimeZoneInfo.get_all_time_zones()
		zones.sort(key=key)
		return zones

class _RegKeyDict(dict):
	def __init__(self, key):
		dict.__init__(self)
		self.key = key
		self.__load_values()

	@classmethod
	def open(cls, *args, **kargs):
		return _RegKeyDict(winreg.OpenKeyEx(*args, **kargs))

	def subkey(self, name):
		return _RegKeyDict(winreg.OpenKeyEx(self.key, name))

	def __load_values(self):
		pairs = [(n, v) for (n, v, t) in self._enumerate_reg_values(self.key)]
		self.update(pairs)

	def subkeys(self):
		return self._enumerate_reg_keys(self.key)

	@staticmethod
	def _enumerate_reg_values(key):
		return _RegKeyDict._enumerate_reg(key, winreg.EnumValue)

	@staticmethod
	def _enumerate_reg_keys(key):
		return _RegKeyDict._enumerate_reg(key, winreg.EnumKey)

	@staticmethod
	def _enumerate_reg(key, func):
		"Enumerates an open registry key as an iterable generator"
		try:
			for index in count():
				yield func(key, index)
		except WindowsError: pass


# for backward compatibility
def deprecated(func, name='Unknown'):
	"""This is a decorator which can be used to mark functions
	as deprecated. It will result in a warning being emmitted
	when the function is used."""
	def newFunc(*args, **kwargs):
		warnings.warn("Call to deprecated function %s." % name,
			category=DeprecationWarning)
		return func(*args, **kwargs)
	newFunc.__name__ = func.__name__
	newFunc.__doc__ = func.__doc__
	newFunc.__dict__.update(func.__dict__)
	return newFunc

GetTimeZoneNames = deprecated(TimeZoneInfo._get_time_zone_key_names, 'GetTimeZoneNames')
GetIndexedTimeZoneNames = deprecated(TimeZoneInfo._get_indexed_time_zone_keys, 'GetIndexedTimeZoneNames')
GetSortedTimeZoneNames = deprecated(TimeZoneInfo.get_sorted_time_zone_names, 'GetSortedTimeZoneNames')
# end backward compatibility

def utcnow():
	"""
	Return the UTC time now with timezone awareness as enabled
	by this module
	>>> now = utcnow()
	"""
	now = datetime.datetime.utcnow()
	now = now.replace(tzinfo=TimeZoneInfo.utc())
	return now

def now():
	"""
	Return the local time now with timezone awareness as enabled
	by this module
	>>> now_local = now()
	"""
	return datetime.datetime.now(TimeZoneInfo.local())

def GetTZCapabilities():
	"""Run a few known tests to determine the capabilities of the time zone database
	on this machine.
	Note Dynamic Time Zone support is not available on any platform at this time; this
	is a limitation of this library, not the platform."""
	tzi = TimeZoneInfo('Mountain Standard Time')
	MissingTZPatch = datetime.datetime(2007,11,2,tzinfo=tzi).utctimetuple() != (2007,11,2,6,0,0,4,306,0)
	DynamicTZSupport = not MissingTZPatch and datetime.datetime(2003,11,2,tzinfo=tzi).utctimetuple() == (2003,11,2,7,0,0,6,306,0)
	del tzi
	return vars()


class DLLHandleCache(object):
	def __init__(self):
		self.__cache = {}

	def __getitem__(self, filename):
		key = filename.lower()
		return self.__cache.setdefault(key, win32api.LoadLibrary(key))

DLLCache = DLLHandleCache()

def resolveMUITimeZone(spec):
	"""Resolve a multilingual user interface resource for the time zone name
	>>> #some pre-amble for the doc-tests to be py2k and py3k aware)
	>>> try: unicode and None
	... except NameError: unicode=str
	...
	>>> import sys
	>>> result = resolveMUITimeZone('@tzres.dll,-110')
	>>> expectedResultType = [type(None),unicode][sys.getwindowsversion() >= (6,)]
	>>> type(result) is expectedResultType
	True

	spec should be of the format @path,-stringID[;comment]
	see http://msdn2.microsoft.com/en-us/library/ms725481.aspx for details
	"""
	pattern = re.compile('@(?P<dllname>.*),-(?P<index>\d+)(?:;(?P<comment>.*))?')
	matcher = pattern.match(spec)
	assert matcher, 'Could not parse MUI spec'

	try:
		handle = DLLCache[matcher.groupdict()['dllname']]
		result = win32api.LoadString(handle, int(matcher.groupdict()['index']))
	except win32api.error:
		result = None
	return result

# from jaraco.util.dictlib 5.3.1
class RangeMap(dict):
	"""
	A dictionary-like object that uses the keys as bounds for a range.
	Inclusion of the value for that range is determined by the
	key_match_comparator, which defaults to less-than-or-equal.
	A value is returned for a key if it is the first key that matches in
	the sorted list of keys.

	One may supply keyword parameters to be passed to the sort function used
	to sort keys (i.e. cmp [python 2 only], keys, reverse) as sort_params.

	Let's create a map that maps 1-3 -> 'a', 4-6 -> 'b'
	>>> r = RangeMap({3: 'a', 6: 'b'})  # boy, that was easy
	>>> r[1], r[2], r[3], r[4], r[5], r[6]
	('a', 'a', 'a', 'b', 'b', 'b')

	Even float values should work so long as the comparison operator
	supports it.
	>>> r[4.5]
	'b'

	But you'll notice that the way rangemap is defined, it must be open-ended on one side.
	>>> r[0]
	'a'
	>>> r[-1]
	'a'

	One can close the open-end of the RangeMap by using undefined_value
	>>> r = RangeMap({0: RangeMap.undefined_value, 3: 'a', 6: 'b'})
	>>> r[0]
	Traceback (most recent call last):
	...
	KeyError: 0

	One can get the first or last elements in the range by using RangeMap.Item
	>>> last_item = RangeMap.Item(-1)
	>>> r[last_item]
	'b'

	.last_item is a shortcut for Item(-1)
	>>> r[RangeMap.last_item]
	'b'

	Sometimes it's useful to find the bounds for a RangeMap
	>>> r.bounds()
	(0, 6)

	RangeMap supports .get(key, default)
	>>> r.get(0, 'not found')
	'not found'

	>>> r.get(7, 'not found')
	'not found'

	"""
	def __init__(self, source, sort_params = {}, key_match_comparator = operator.le):
		dict.__init__(self, source)
		self.sort_params = sort_params
		self.match = key_match_comparator

	def __getitem__(self, item):
		sorted_keys = sorted(list(self.keys()), **self.sort_params)
		if isinstance(item, RangeMap.Item):
			result = self.__getitem__(sorted_keys[item])
		else:
			key = self._find_first_match_(sorted_keys, item)
			result = dict.__getitem__(self, key)
			if result is RangeMap.undefined_value:
				raise KeyError(key)
		return result

	def get(self, key, default=None):
		"""
		Return the value for key if key is in the dictionary, else default.
		If default is not given, it defaults to None, so that this method
		never raises a KeyError.
		"""
		try:
			return self[key]
		except KeyError:
			return default

	def _find_first_match_(self, keys, item):
		is_match = lambda k: self.match(item, k)
		matches = list(filter(is_match, keys))
		if matches:
			return matches[0]
		raise KeyError(item)

	def bounds(self):
		sorted_keys = sorted(list(self.keys()), **self.sort_params)
		return (
			sorted_keys[RangeMap.first_item],
			sorted_keys[RangeMap.last_item],
		)

	# some special values for the RangeMap
	undefined_value = type(str('RangeValueUndefined'), (object,), {})()
	class Item(int): pass
	first_item = Item(0)
	last_item = Item(-1)