isoformat中的时区域 [英] Time zone field in isoformat

问题描述

我的时间戳应该在EST中：

  2014-10-06T18：06：40-04 ：56 
  

我明白这第一部分： 2014-10-06T18：06 ：40 ，但不是 -04：56 。

-04：56 是什么意思？

这是我如何获得时间戳：

  import datetime 
 start_time = datetime.datetime（year = 2014 ，
 month = 10，
 day = 6，
 hour = 18，
 tzinfo = pytz.timezone（'US / Eastern'）
 end_time = start_time + datetime.timedelta（seconds = 400）
  

然后：

  end_time.isoformat（）
  

返回：

  2014-10-06T18：06：40-04：56 
  pre> 
 
解决方案
问题是  pytz  ：
 
 
 ...与tzinfo实现的文档Python API不同;如果要创建本地的wallclock时间，您需要使用本文档中记录的 localize（）方法... 
 
 
进一步说，它说：
 
 
不幸的是使用标准datetime构造函数的tzinfo参数不起作用with pytz for many timezones。
 
 
 
 
 
 >>> datetime（2002，10，27，12，0，0，tzinfo = amsterdam）.strftime（fmt）
'2002-10-27 12:00:00 LMT + 0020'
  
 
 
 
 
 
 
所以，您需要使用文档建议 - 使用规范化，构建UTC时间并使用 astimezone 等。您想要的是什么取决于您正在尝试做什么。例如：
 >>> from datetime import datetime 
>>>>来自pytz import timezone 
>>>> utc = timezone（'UTC'）
>>>>东部=时区（'美国/东部）
>>>> datetime（2014，10，6，18，tzinfo = east）.isoformat（）
'2014-10-06T18：00：00-04：56'
>>> east.normalize（datetime（2014，10，6，18，tzinfo = east））。isoformat（）
'2014-10-06T18：56：00-04：00'
>> > datetime（2014，10，6，18，tzinfo = utc）.astimezone（east）.isoformat（）
'2014-10-06T14：00：00-04：00'
>> > east.localize（datetime（2014，10，6，18））。isoformat（）
'2014-10-06T18：00：00-04：00'
  / pre> 
 
 
我认为这是你想要的最后一个。作为本地化的文档说：
 
 
将天真的时间转换为本地时间。 / p> 
 
 
此方法应用于构建localtimes，而不是将tzinfo参数传递给datetime构造函数，而不是
。
 
 
我认为构建当地时间正是您想要的。
 
 
 
 
 
 
如果您想知道为什么 ...好吧，如果您查看Olson数据库中的数据，或者只打印出 east._utcoffset 你会看到-1天，+68640分钟。那是19.0166+小时，而不是19.为什么？因为每个时区都以起始偏移量定义，从那里进行调整。东方是根据纽约时间1883年11月18日12:03:58的时区，此时是GMT的-04：56：02。从1920年开始的日期调整将减去额外的00:03:58。当然，对于DST来说，每年都会有一个小时的调整。所以，截至目前，东方是-04：00，但不知道应该代表什么日期，是-04：56。而且，因为 datetime 只是要求一个时区作为其偏移量，而不是在特定时间的偏移量，那就是它获得的。
 
 
 
 
 
 
最后一件事：EST是东部标准时间，这是-05：00。这不是2014年10月6日美国任何地点的时区，因为在2014年，美国的夏令时到11月2日。 （以前在印第安那州曾经是美国东部时间在夏天的县，但不再是。）你要找的是EDT，东方夏令时，这是-04：00。或者，当然，ET是夏天的EDT，冬天的EST，这是你从查找'US / Eastern'或'America / New_York'。
 
I have a timestamp that is supposed to be in EST:
2014-10-06T18:06:40-04:56
I understand this first part: 2014-10-06T18:06:40, but not -04:56. 

What does -04:56 mean here?`

Here is how I got that timestamp:
import datetime
start_time = datetime.datetime(year  = 2014, 
                               month = 10, 
                               day   = 6, 
                               hour  = 18, 
                               tzinfo = pytz.timezone('US/Eastern'))
end_time   = start_time + datetime.timedelta(seconds=400)
And then:
end_time.isoformat()
returns: 
2014-10-06T18:06:40-04:56

解决方案
The problem is that pytz:

  
… differs from the documented Python API for tzinfo implementations; if you want to create local wallclock times you need to use the localize() method documented in this document …
Further down, it says:

  
Unfortunately using the tzinfo argument of the standard datetime constructors "does not work" with pytz for many timezones.


>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=amsterdam).strftime(fmt)
'2002-10-27 12:00:00 LMT+0020'




So, you need to do what the docs suggest—using normalize, constructing UTC times and using astimezone, etc. Which one you want depends on exactly what you're trying to do. For example:
>>> from datetime import datetime
>>> from pytz import timezone
>>> utc = timezone('UTC')
>>> eastern = timezone('US/Eastern')
>>> datetime(2014, 10, 6, 18, tzinfo=eastern).isoformat()
'2014-10-06T18:00:00-04:56'
>>> eastern.normalize(datetime(2014, 10, 6, 18, tzinfo=eastern)).isoformat()
'2014-10-06T18:56:00-04:00'
>>> datetime(2014, 10, 6, 18, tzinfo=utc).astimezone(eastern).isoformat()
'2014-10-06T14:00:00-04:00'
>>> eastern.localize(datetime(2014, 10, 6, 18)).isoformat()
'2014-10-06T18:00:00-04:00'
I think it's the last you want. As the docs for localize say:

  
Convert naive time to local time.
  
  
This method should be used to construct localtimes, rather
  than passing a tzinfo argument to a datetime constructor.
And I think constructing a local time is exactly what you wanted here.



If you're wondering why… well, if you look at the data that's in your Olson database, or just print out eastern._utcoffset, you'll see -1 day, +68640 minutes. That's 19.0166+ hours, not 19. Why? Because every timezone is defined with its starting offset, with adjustments from there. Eastern is based on New York's timezone as of 1883 Nov 18 12:03:58, at which point it was -04:56:02 from GMT. There's an adjustment for dates starting in 1920 that subtracts the extra 00:03:58. And of course the yearly adjustments back and forth one hour for DST. So, as of right now, Eastern is -04:00, but without any idea of what date it's supposed to represent, it's -04:56. And, because datetime just asks a timezone for its offset, rather than its offset at a particular time, that's what it gets.



One last thing: EST is Eastern Standard Time, which is -05:00. That's not the time zone of any location in the US on 6 October 2014, because in 2014, the US's daylight saving time goes to 2 November. (There used to be counties in Indiana that were on EST during the summer, but there no longer are.) What you're looking for is EDT, Eastern Daylight Time, which is -04:00. Or, of course, ET, which is EDT during the summer and EST during the winter, which is what you get from looking up 'US/Eastern' or 'America/New_York'.

                        
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