使用时区，Python打印正确的时间 [英] Printing correct time using timezones, Python
问题描述
好的，我们今天没有好的一天。
Ok, we are not having a good day today.
将正确的tzinfo对象附加到datetime实例，然后你strftime（）它，它STILL出来在UTC，似乎忽略了我附加的美丽的tzinfo对象。
When you attach the correct tzinfo object to a datetime instance, and then you strftime() it, it STILL comes out in UTC, seemingly ignoring the beautiful tzinfo object I attached to it.
# python 2.5.4
now = datetime.now()
print now.strftime( "%a %b %d %X" ) # %X is "locale's appropriate time rep"
pst = now.replace( tzinfo=Pacific )
print pst.strftime( "%a %b %d %X" )
我们得到：
Mon Jan 18 17:30:16
Mon Jan 18 17:30:16
我发现如果我添加％z，我可以添加它应该计算的差异：
I found if I add %z, I can add the difference its supposed to have computed:
Mon Jan 18 17:32:38
Mon Jan 18 17:32:38 -0800
它只是在-8那里，就好像说，你自己动手做，
It just tacks on the -8 there, as if to say, "you do it yourself, foo."
但是我希望strftime（）只需要给我一个字符串，并且可以使用PRECOMPUTED LOCAL TIME。
But I want strftime() to simply give me a string WITH PRECOMPUTED LOCAL TIME.
当我strftime（）它时，我如何获得strftime（）来为我做小时减法数学？
How can I get strftime() to do the hour subtraction math for me when I strftime() it?
完整的代码我是使用在下面。
The full code I'm using is below.
from datetime import tzinfo, timedelta, datetime
ZERO = timedelta(0)
HOUR = timedelta(hours=1)
# A UTC class.
class UTC(tzinfo):
"""UTC"""
def utcoffset(self, dt):
return ZERO
def tzname(self, dt):
return "UTC"
def dst(self, dt):
return ZERO
utc = UTC()
# A class building tzinfo objects for fixed-offset time zones.
# Note that FixedOffset(0, "UTC") is a different way to build a
# UTC tzinfo object.
class FixedOffset(tzinfo):
"""Fixed offset in minutes east from UTC."""
def __init__(self, offset, name):
self.__offset = timedelta(minutes = offset)
self.__name = name
def utcoffset(self, dt):
return self.__offset
def tzname(self, dt):
return self.__name
def dst(self, dt):
return ZERO
# A class capturing the platform's idea of local time.
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 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, -1)
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
# In the US, DST starts at 2am (standard time) on the first Sunday in April.
DSTSTART = datetime(1, 4, 1, 2)
# and ends at 2am (DST time; 1am standard time) on the last Sunday of Oct.
# which is the first Sunday on or after Oct 25.
DSTEND = datetime(1, 10, 25, 1)
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
# Find first Sunday in April & the last in October.
start = first_sunday_on_or_after(DSTSTART.replace(year=dt.year))
end = first_sunday_on_or_after(DSTEND.replace(year=dt.year))
# Can't compare naive to aware objects, so strip the timezone from
# dt first.
if start <= dt.replace(tzinfo=None) < end:
return HOUR
else:
return ZERO
Eastern = USTimeZone(-5, "Eastern", "EST", "EDT")
#Central = USTimeZone(-6, "Central", "CST", "CDT")
#Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
Pacific = USTimeZone(-8, "Pacific", "PST", "PDT")
now = datetime.now()
print now.strftime( "%a %b %d %X %z" )
pst = now.replace( tzinfo=Pacific )
print pst.strftime( "%a %b %d %X %z" )
推荐答案
.replace 没有计算：它只是替换新的返回对象中的一个或多个字段，同时从所调用的对象复制所有其他字段。
.replace does no computation: it simply replaces one or more field in the new returned object, while copying all others from the object it's called on.
如果我明白你的情况是正确的，你从一个datetime对象开始，你知道（通过其他方式）是UTC，但不知道自己（有一个tzinfo属性没有，意思是我完全没有什么时间
If I understand your situation correctly, you start with a datetime object which you know (through other means) is UTC, but doesn't know that itself (is has a tzinfo attribute of None, meaning "I'm totally clueless regarding what timezone I'm in).
所以，第一个，您可以从输入时区 - 天真的对象中进行时区识别，以便通知它是在时区UTC（所有其他字段只是被复制）：
So, first, you make a timezone-aware from your input timezone-naive object, in order to inform it that it's in timezone UTC (all other fields just get copied over):
aware = naive.replace(tzinfo=utc)
然后，您可以请求有关时区的计算，并因此打印：
Then, you can request computations regarding timezones, and printing in consequence:
print aware.astimezone(Pacific).strftime('%a %b %d %X %z')
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