python/lib/django-1.5/django/utils/tzinfo.py

   1 "Implementation of tzinfo classes for use with datetime.datetime."
   2
   3 from __future__ import unicode_literals
   4
   5 import time
   6 from datetime import timedelta, tzinfo
   7
   8 from django.utils.encoding import force_str, force_text, DEFAULT_LOCALE_ENCODING
   9
  10 # Python's doc say: "A tzinfo subclass must have an __init__() method that can
  11 # be called with no arguments". FixedOffset and LocalTimezone don't honor this
  12 # requirement. Defining __getinitargs__ is sufficient to fix copy/deepcopy as
  13 # well as pickling/unpickling.
  14
  15 class FixedOffset(tzinfo):
  16     "Fixed offset in minutes east from UTC."
  17     def __init__(self, offset):
  18         if isinstance(offset, timedelta):
  19             self.__offset = offset
  20             offset = self.__offset.seconds // 60
  21         else:
  22             self.__offset = timedelta(minutes=offset)
  23
  24         sign = '-' if offset < 0 else '+'
  25         self.__name = "%s%02d%02d" % (sign, abs(offset) / 60., abs(offset) % 60)
  26
  27     def __repr__(self):
  28         return self.__name
  29
  30     def __getinitargs__(self):
  31         return self.__offset,
  32
  33     def utcoffset(self, dt):
  34         return self.__offset
  35
  36     def tzname(self, dt):
  37         return self.__name
  38
  39     def dst(self, dt):
  40         return timedelta(0)
  41
  42 # This implementation is used for display purposes. It uses an approximation
  43 # for DST computations on dates >= 2038.
  44
  45 # A similar implementation exists in django.utils.timezone. It's used for
  46 # timezone support (when USE_TZ = True) and focuses on correctness.
  47
  48 class LocalTimezone(tzinfo):
  49     "Proxy timezone information from time module."
  50     def __init__(self, dt):
  51         tzinfo.__init__(self)
  52         self.__dt = dt
  53         self._tzname = self.tzname(dt)
  54
  55     def __repr__(self):
  56         return force_str(self._tzname)
  57
  58     def __getinitargs__(self):
  59         return self.__dt,
  60
  61     def utcoffset(self, dt):
  62         if self._isdst(dt):
  63             return timedelta(seconds=-time.altzone)
  64         else:
  65             return timedelta(seconds=-time.timezone)
  66
  67     def dst(self, dt):
  68         if self._isdst(dt):
  69             return timedelta(seconds=-time.altzone) - timedelta(seconds=-time.timezone)
  70         else:
  71             return timedelta(0)
  72
  73     def tzname(self, dt):
  74         try:
  75             return force_text(time.tzname[self._isdst(dt)],
  76                                  DEFAULT_LOCALE_ENCODING)
  77         except UnicodeDecodeError:
  78             return None
  79
  80     def _isdst(self, dt):
  81         tt = (dt.year, dt.month, dt.day,
  82               dt.hour, dt.minute, dt.second,
  83               dt.weekday(), 0, 0)
  84         try:
  85             stamp = time.mktime(tt)
  86         except (OverflowError, ValueError):
  87             # 32 bit systems can't handle dates after Jan 2038, and certain
  88             # systems can't handle dates before ~1901-12-01:
  89             #
  90             # >>> time.mktime((1900, 1, 13, 0, 0, 0, 0, 0, 0))
  91             # OverflowError: mktime argument out of range
  92             # >>> time.mktime((1850, 1, 13, 0, 0, 0, 0, 0, 0))
  93             # ValueError: year out of range
  94             #
  95             # In this case, we fake the date, because we only care about the
  96             # DST flag.
  97             tt = (2037,) + tt[1:]
  98             stamp = time.mktime(tt)
  99         tt = time.localtime(stamp)
 100         return tt.tm_isdst > 0