将UTC中的时间与东部时间的Python进行比较 [英] Comparing a time in UTC with a time in Eastern time using Python

问题描述

我正在尝试使用Python datetime 模块进行两次比较，但我似乎无法创建时区感知 / code>对象在UTC。

I'm trying to compare two times using the Python datetime module, but I can't seem to create a timezone-aware time object in UTC.

>>> import pytz, datetime
>>> UTC_TZ = pytz.utc
>>> EASTERN_TZ = pytz.timezone('America/New_York')
>>> d1 = datetime.time(10, tzinfo = UTC_TZ)
>>> d1
datetime.time(10, 0, tzinfo=<UTC>)
>>> d2 = datetime.time(10, tzinfo = EASTERN_TZ)
>>> d2
datetime.time(10, 0, tzinfo=<DstTzInfo 'America/New_York' EST-1 day, 19:00:00 STD>)
>>> d1 < d2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't compare offset-naive and offset-aware times

这是一个bug？有没有特殊的UTC时区需要使用？发生什么事？

Is this a bug? Is there a special UTC timezone I need to use? What's going on?

推荐答案

所有这一切都归功于wberry困惑，但为了有一个简明的答案，

All credit to wberry for puzzling this out, but in the interest of having a concise answer, I'll summarize it here.

根据datetime文档，当比较两个datetime.time对象时：如果两个比较都知道并具有不同的tzinfo属性，则比较是第一个通过减去它们的UTC偏移量（从self.utcoffset（）获得）进行调整

According to the datetime docs, when comparing two datetime.time objects: "If both comparands are aware and have different tzinfo attributes, the comparands are first adjusted by subtracting their UTC offsets (obtained from self.utcoffset())"

在您给出的示例中，比较引发TypeError，因为EASTERN_TZ.utcoffset（）返回None 。 utcoffset是None，因为美国东部观察夏令时，所以与UTC的时间偏移取决于datetime.time中不可用的日期。

In the example you gave, the comparison throws the TypeError because EASTERN_TZ.utcoffset() returns None. utcoffset is None because the eastern US observes Daylight Savings Time and so the time offset from UTC depends on the date which isn't available in datetime.time.

你应该使用用于跨时区比较的datetime.datetime对象：

You should use datetime.datetime objects for cross-timezone comparisons:

>>> import pytz, datetime
>>> UTC_TZ = pytz.utc
>>> EASTERN_TZ = pytz.timezone('America/New_York')
>>> d1 = datetime.datetime(2012, 1, 1, 10, 0, tzinfo=UTC_TZ)
>>> d2 = datetime.datetime(2012, 1, 1, 10, 0, tzinfo=EASTERN_TZ)
>>> d1 < d2
True

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