datetime.tzinfo基本日期和时间类型的tzinfo对象详解(24)Python语言(必读进阶学习教程)(参考资料)

from datetime import tzinfo, timedelta, datetime 

ZERO = timedelta(0) 
HOUR = timedelta(hours=1) 
SECOND = timedelta(seconds=1) 
# A class capturing the platform's idea of local time. 
# (May result in wrong values on historical times in 
# timezones where UTC offset and/or the DST rules had 
# changed in the past.) 
import time as _time 

STDOFFSET = timedelta(seconds = -_time.timezone) 
if _time.daylight: 
    DSTOFFSET = timedelta(seconds = -_time.altzone) 
else: 
    DSTOFFSET = STDOFFSET 
DSTDIFF = DSTOFFSET - STDOFFSET 

class LocalTimezone(tzinfo): 
    def fromutc(self, dt): 
        assert dt.tzinfo is 
        self stamp = (dt - datetime(1970, 1, 1, tzinfo=self)) // SECOND 
        args = _time.localtime(stamp)[:6] 
        dst_diff = DSTDIFF // SECOND 
        # Detect fold 
        fold = (args == _time.localtime(stamp - dst_diff)) 
        return datetime(*args, microsecond=dt.microsecond, tzinfo=self, fold=fold) 
    def utcoffset(self, dt): 
        if self._isdst(dt): 
            return DSTOFFSET 
        else: 
            return STDOFFSET 
    def dst(self, dt): 
        if self._isdst(dt): 
            return DSTDIFF 
        else: 
            return ZERO 
    def tzname(self, dt): 
        return _time.tzname[self._isdst(dt)] 
    def _isdst(self, dt): 
        tt = (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, dt.weekday(), 0, 0) 
        stamp = _time.mktime(tt) 
        tt = _time.localtime(stamp) 
        return tt.tm_isdst > 0 
Local = LocalTimezone() 
# A complete implementation of current DST rules for major US time zones. 
def first_sunday_on_or_after(dt): 
    days_to_go = 6 - dt.weekday() 
    if days_to_go: 
        dt += timedelta(days_to_go) 
        return dt 

# US DST Rules 
# 
# This is a simplified (i.e., wrong for a few cases) set of rules for US 
# DST start and end times. For a complete and up-to-date set of DST rules 
# and timezone definitions, visit the Olson Database (or try pytz): 
# http://www.twinsun.com/tz/tz-link.htm # http://sourceforge.net/projects/pytz/ (might not be up-to-date) 
# 
# In the US, since 2007, DST starts at 2am (standard time) on the second 
# Sunday in March, which is the first Sunday on or after Mar 8. 

DSTSTART_2007 = datetime(1, 3, 8, 2) 

# and ends at 2am (DST time) on the first Sunday of Nov. 

DSTEND_2007 = datetime(1, 11, 1, 2) 

# From 1987 to 2006, DST used to start at 2am (standard time) on the first 
# Sunday in April and to end at 2am (DST time) on the last 
# Sunday of October, which is the first Sunday on or after Oct 25. 

DSTSTART_1987_2006 = datetime(1, 4, 1, 2) 
DSTEND_1987_2006 = datetime(1, 10, 25, 2) 

# From 1967 to 1986, DST used to start at 2am (standard time) on the last 
# Sunday in April (the one on or after April 24) and to end at 2am (DST time) 
# on the last Sunday of October, which is the first Sunday 
# on or after Oct 25. 
DSTSTART_1967_1986 = datetime(1, 4, 24, 2) 
DSTEND_1967_1986 = DSTEND_1987_2006 
def us_dst_range(year): 
# Find start and end times for US DST. For years before 1967, return 
# start = end for no DST. 
    if 2006 < year: 
        dststart, dstend = DSTSTART_2007, DSTEND_2007 
    elif 1986 < year < 2007: 
        dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006 
    elif 1966 < year < 1987: 
        dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986 
    else: 
        return (datetime(year, 1, 1), ) * 2 

    start = first_sunday_on_or_after(dststart.replace(year=year)) 
    end = first_sunday_on_or_after(dstend.replace(year=year)) 
    return start, end 

class USTimeZone(tzinfo): 
    def __init__(self, hours, reprname, stdname, dstname): 
        self.stdoffset = timedelta(hours=hours) 
        self.reprname = reprname 
        self.stdname = stdname 
        self.dstname = dstname 

   def __repr__(self): 
       return self.reprname 

   def tzname(self, dt): 
       if self.dst(dt): 
           return self.dstname 
       else: 
           return self.stdname 

   def utcoffset(self, dt): 
       return self.stdoffset + self.dst(dt) 

   def dst(self, dt): 
       if dt is None or dt.tzinfo is None: 
           # An exception may be sensible here, in one or both cases. 
           # It depends on how you want to treat them. The default 
           # fromutc() implementation (called by the default astimezone() 
           # implementation) passes a datetime with dt.tzinfo is self. 
           return ZERO 
       assert dt.tzinfo is self 
       start, end = us_dst_range(dt.year) 
       # Can't compare naive to aware objects, so strip the timezone from 
       # dt first. 
       dt = dt.replace(tzinfo=None) 
       if start + HOUR <= dt < end - HOUR: 
           # DST is in effect. 
           return HOUR 
       if end - HOUR <= dt < end: 
           # Fold (an ambiguous hour): use dt.fold to disambiguate. 
           return ZERO if dt.fold else HOUR 
       if start <= dt < start + HOUR: 
           # Gap (a non-existent hour): reverse the fold rule. 
           return HOUR if dt.fold else ZERO 
       # DST is off. 
       return ZERO 
   def fromutc(self, dt): 
       assert dt.tzinfo is self 
       start, end = us_dst_range(dt.year) 
       start = start.replace(tzinfo=self) 
       end = end.replace(tzinfo=self) 
       std_time = dt + self.stdoffset 
       dst_time = std_time + HOUR 
       if end <= dst_time < end + HOUR: 
           # Repeated hour 
           return std_time.replace(fold=1) 
       if std_time < start or dst_time >= end: 
           # Standard time 
           return std_time 
       if start <= std_time < end - HOUR: 
           # Daylight saving time 
           return dst_time 
Eastern = USTimeZone(-5, "Eastern", "EST", "EDT") 
Central = USTimeZone(-6, "Central", "CST", "CDT") 
Mountain = USTimeZone(-7, "Mountain", "MST", "MDT") 
Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")

  UTC   3:MM  4:MM  5:MM  6:MM  7:MM  8:MM
  EST  22:MM 23:MM  0:MM  1:MM  2:MM  3:MM
  EDT  23:MM  0:MM  1:MM  2:MM  3:MM  4:MM

start  22:MM 23:MM  0:MM  1:MM  3:MM  4:MM

  end  23:MM  0:MM  1:MM  1:MM  2:MM  3:MM