问题描述

我正在阅读不太完整的 pytz 文档，但我一直坚持理解其中的一部分.

I'm reading the not so complete pytz documentation and I'm stuck on understand one part of it.

时区之间的转换也需要特别注意.这也需要使用 normalize 方法来保证转换正确.

Converting between timezones also needs special attention. This also needs to use the normalize method to ensure the conversion is correct.

>>> utc_dt = utc.localize(datetime.utcfromtimestamp(1143408899))
>>> utc_dt.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'
>>> au_tz = timezone('Australia/Sydney')
>>> au_dt = au_tz.normalize(utc_dt.astimezone(au_tz))
>>> au_dt.strftime(fmt)
'2006-03-27 08:34:59 EST+1100'
>>> utc_dt2 = utc.normalize(au_dt.astimezone(utc))
>>> utc_dt2.strftime(fmt)
'2006-03-26 21:34:59 UTC+0000'

我使用 normalize 尝试了这个示例 without，结果还是一样.在我看来，这个例子并没有真正解释为什么在不同时区的datetime对象之间进行转换时，我们必须使用normalize.

I tried this very example without using normalize and it turned out just the same. In my opinion this example doesn't really explain why we have to use normalize when converting between datetime objects in different timezones.

谁能给我一个示例(如上面的示例)，当不使用 normalize 时结果会有所不同.

Would someone please give me an example (like the one above) where the result differs when not using normalize.

谢谢

推荐答案

来自 pytz 文档:

From the pytz documentation:

此外，如果您对跨越 DST 边界的本地时间执行日期算术，则结果可能位于不正确的时区(即，从 2002-10-27 1:00 EST 减去 1 分钟，得到 2002-10-27 0:59 EST 而不是正确的 2002-10-27 1:59 EDT).提供了一个 normalize() 方法来纠正这个问题.不幸的是，如果不修改 Python 日期时间实现，就无法解决这些问题.

In addition, if you perform date arithmetic on local times that cross DST boundaries, the results may be in an incorrect timezone (ie. subtract 1 minute from 2002-10-27 1:00 EST and you get 2002-10-27 0:59 EST instead of the correct 2002-10-27 1:59 EDT). A normalize() method is provided to correct this. Unfortunately these issues cannot be resolved without modifying the Python datetime implementation.

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