Doc/includes/tzinfo-examples.py

   1 from datetime import tzinfo, timedelta, datetime
   2
   3 ZERO = timedelta(0)
   4 HOUR = timedelta(hours=1)
   5
   6 # A UTC class.
   7
   8 class UTC(tzinfo):
   9     """UTC"""
  10
  11     def utcoffset(self, dt):
  12         return ZERO
  13
  14     def tzname(self, dt):
  15         return "UTC"
  16
  17     def dst(self, dt):
  18         return ZERO
  19
  20 utc = UTC()
  21
  22 # A class building tzinfo objects for fixed-offset time zones.
  23 # Note that FixedOffset(0, "UTC") is a different way to build a
  24 # UTC tzinfo object.
  25
  26 class FixedOffset(tzinfo):
  27     """Fixed offset in minutes east from UTC."""
  28
  29     def __init__(self, offset, name):
  30         self.__offset = timedelta(minutes = offset)
  31         self.__name = name
  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 ZERO
  41
  42 # A class capturing the platform's idea of local time.
  43
  44 import time as _time
  45
  46 STDOFFSET = timedelta(seconds = -_time.timezone)
  47 if _time.daylight:
  48     DSTOFFSET = timedelta(seconds = -_time.altzone)
  49 else:
  50     DSTOFFSET = STDOFFSET
  51
  52 DSTDIFF = DSTOFFSET - STDOFFSET
  53
  54 class LocalTimezone(tzinfo):
  55
  56     def utcoffset(self, dt):
  57         if self._isdst(dt):
  58             return DSTOFFSET
  59         else:
  60             return STDOFFSET
  61
  62     def dst(self, dt):
  63         if self._isdst(dt):
  64             return DSTDIFF
  65         else:
  66             return ZERO
  67
  68     def tzname(self, dt):
  69         return _time.tzname[self._isdst(dt)]
  70
  71     def _isdst(self, dt):
  72         tt = (dt.year, dt.month, dt.day,
  73               dt.hour, dt.minute, dt.second,
  74               dt.weekday(), 0, -1)
  75         stamp = _time.mktime(tt)
  76         tt = _time.localtime(stamp)
  77         return tt.tm_isdst > 0
  78
  79 Local = LocalTimezone()
  80
  81
  82 # A complete implementation of current DST rules for major US time zones.
  83
  84 def first_sunday_on_or_after(dt):
  85     days_to_go = 6 - dt.weekday()
  86     if days_to_go:
  87         dt += timedelta(days_to_go)
  88     return dt
  89
  90
  91 # US DST Rules
  92 #
  93 # This is a simplified (i.e., wrong for a few cases) set of rules for US
  94 # DST start and end times. For a complete and up-to-date set of DST rules
  95 # and timezone definitions, visit the Olson Database (or try pytz):
  96 # http://www.twinsun.com/tz/tz-link.htm
  97 # http://sourceforge.net/projects/pytz/ (might not be up-to-date)
  98 #
  99 # In the US, since 2007, DST starts at 2am (standard time) on the second
 100 # Sunday in March, which is the first Sunday on or after Mar 8.
 101 DSTSTART_2007 = datetime(1, 3, 8, 2)
 102 # and ends at 2am (DST time; 1am standard time) on the first Sunday of Nov.
 103 DSTEND_2007 = datetime(1, 11, 1, 1)
 104 # From 1987 to 2006, DST used to start at 2am (standard time) on the first
 105 # Sunday in April and to end at 2am (DST time; 1am standard time) on the last
 106 # Sunday of October, which is the first Sunday on or after Oct 25.
 107 DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
 108 DSTEND_1987_2006 = datetime(1, 10, 25, 1)
 109 # From 1967 to 1986, DST used to start at 2am (standard time) on the last
 110 # Sunday in April (the one on or after April 24) and to end at 2am (DST time;
 111 # 1am standard time) on the last Sunday of October, which is the first Sunday
 112 # on or after Oct 25.
 113 DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
 114 DSTEND_1967_1986 = DSTEND_1987_2006
 115
 116 class USTimeZone(tzinfo):
 117
 118     def __init__(self, hours, reprname, stdname, dstname):
 119         self.stdoffset = timedelta(hours=hours)
 120         self.reprname = reprname
 121         self.stdname = stdname
 122         self.dstname = dstname
 123
 124     def __repr__(self):
 125         return self.reprname
 126
 127     def tzname(self, dt):
 128         if self.dst(dt):
 129             return self.dstname
 130         else:
 131             return self.stdname
 132
 133     def utcoffset(self, dt):
 134         return self.stdoffset + self.dst(dt)
 135
 136     def dst(self, dt):
 137         if dt is None or dt.tzinfo is None:
 138             # An exception may be sensible here, in one or both cases.
 139             # It depends on how you want to treat them.  The default
 140             # fromutc() implementation (called by the default astimezone()
 141             # implementation) passes a datetime with dt.tzinfo is self.
 142             return ZERO
 143         assert dt.tzinfo is self
 144
 145         # Find start and end times for US DST. For years before 1967, return
 146         # ZERO for no DST.
 147         if 2006 < dt.year:
 148             dststart, dstend = DSTSTART_2007, DSTEND_2007
 149         elif 1986 < dt.year < 2007:
 150             dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
 151         elif 1966 < dt.year < 1987:
 152             dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
 153         else:
 154             return ZERO
 155
 156         start = first_sunday_on_or_after(dststart.replace(year=dt.year))
 157         end = first_sunday_on_or_after(dstend.replace(year=dt.year))
 158
 159         # Can't compare naive to aware objects, so strip the timezone from
 160         # dt first.
 161         if start <= dt.replace(tzinfo=None) < end:
 162             return HOUR
 163         else:
 164             return ZERO
 165
 166 Eastern  = USTimeZone(-5, "Eastern",  "EST", "EDT")
 167 Central  = USTimeZone(-6, "Central",  "CST", "CDT")
 168 Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
 169 Pacific  = USTimeZone(-8, "Pacific",  "PST", "PDT")