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, 0) 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") 170
