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Python Open Source » Windows » pyExcelerator 
pyExcelerator » pywin32 214 » win32 » lib » 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.

  Currently, this module only supports the Windows NT line of products
and not Windows 95/98/Me.

  This module may be tested using the doctest module.

  Written by Jason R. Coombs (jaraco@jaraco.com).
  Copyright  2003-2009.
  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)
'(GMT-05:00) Eastern Time (US & Canada)'

>>> gmt = win32timezone.TimeZoneInfo('GMT Standard Time', True)
>>> str(gmt.displayName)
'(GMT) Greenwich Mean Time : 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, 'fran\xc3\xa7ais'.decode('utf-8'))

"""
from __future__ import generators

__author__ = 'Jason R. Coombs <jaraco@jaraco.com>'
__version__ = '$Revision: 1.28 $'[11:-2]
__sccauthor__ = '$Author: jaraco $'[9:-2]
__date__ = '$Date: 2009/03/25 00:29:43 $'[10:-2]

import os
import _winreg
import struct
import datetime
import win32api
import re
import sys
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 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', unicode),
    ('standard_start', SYSTEMTIME),
    ('standard_bias', int),
    ('daylight_name', unicode),
    ('daylight_start', SYSTEMTIME),
    ('daylight_bias', int),
  ]

class DYNAMIC_TIME_ZONE_INFORMATION(_SimpleStruct):
  _fields_ = TIME_ZONE_INFORMATION._fields_ + [
    ('key_name', unicode),
    ('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.
  """

  # 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, basestring):
      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):
    try:
      info = key.subkey('Dynamic DST')
    except WindowsError:
      return
    del info['FirstEntry']
    del info['LastEntry']
    years = map(int, info.keys())
    values = map(TimeZoneDefinition, 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), descending, 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):
    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[RangeItemLast()])
    
  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):
    try:
      dstStart = self.GetDSTStartTime(dt.year)
      dstEnd = self.GetDSTEndTime(dt.year)
      
      if dstStart < dstEnd:
        inDaylightSavings = dstStart <= dt.replace(tzinfo=None) < dstEnd
      else:
        # in the southern hemisphere, daylight savings time
        #  typically ends before it begins in a given year.
        inDaylightSavings = not (dstEnd < dt.replace(tzinfo=None) <= dstStart)
    except ValueError:
      # there was an error parsing the time zone, which is normal when a
      #  start and end time are not specified.
      inDaylightSavings = False

    return inDaylightSavings

  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
  ...
  >>> 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, e:
    result = None
  return result

# the following code implements a RangeMap and its support classes

ascending = lambda a, b: b < a
def descending(a, b):
  return not ascending(a, b)

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
  keyMatchComparator, which defaults to greater-than-or-equal.
  A value is returned for a key if it is the first key that matches in
  the sorted list of keys.  By default, keys are sorted in ascending
  order, but can be sorted in any other order using the keySortComparator.

  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')

  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 RangeValueUndefined
  >>> r = RangeMap({0: RangeValueUndefined(), 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 RangeItem
  >>> last_item = RangeItem(-1)
  >>> r[last_item]
  'b'

  >>> r[RangeItemLast()]
  'b'

  >>> r.bounds()
  (0, 6)
  
  """
  def __init__(self, source, keySortComparator = ascending, keyMatchComparator = operator.le):
    dict.__init__(self, source)
    self.sort = keySortComparator
    self.match = keyMatchComparator

  def _get_sorted_keys(self):
    sortedKeys = self.keys()
    reverse = self.match != operator.le
    sortedKeys.sort(reverse=reverse)
    return sortedKeys

  def __getitem__(self, item):
    sortedKeys = self._get_sorted_keys()
    if isinstance(item, RangeItem):
      result = self.__getitem__(sortedKeys[item])
    else:
      key = self._find_first_match_(sortedKeys, item)
      result = dict.__getitem__(self, key)
      if isinstance(result, RangeValueUndefined): raise KeyError(key)
    return result

  def _find_first_match_(self, keys, item):
    is_match = lambda k: self.match(item, k)
    # use of ifilter here would be more efficent
    matches = [k for k in keys if is_match(k)]
    if matches:
      return matches[0]
    raise KeyError(item)

  def bounds(self):
    sortedKeys = self._get_sorted_keys()
    return sortedKeys[RangeItemFirst()], sortedKeys[RangeItemLast()]

class RangeValueUndefined(object): pass
class RangeItem(int):
  def __new__(cls, value):
    return int.__new__(cls, value)
class RangeItemFirst(RangeItem):
  def __new__(cls):
    return RangeItem.__new__(cls, 0)
class RangeItemLast(RangeItem):
  def __new__(cls):
    return RangeItem.__new__(cls, -1)
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