如何仅使用标准库将 UTC 日期时间转换为本地日期时间? [英] How to convert a UTC datetime to a local datetime using only standard library?

问题描述

我有一个使用 datetime.utcnow() 创建并保存在数据库中的 python datetime 实例.

为了显示，我想将从数据库中检索到的 datetime 实例转换为使用默认本地时区的本地 datetime(即，就好像 datetime 是使用 datetime.now() 创建的.

如何仅使用 python 标准库(例如，没有 pytz 依赖项)将 UTC datetime 转换为本地 datetime?

似乎一种解决方案是使用 datetime.astimezone(tz)，但是如何获得默认的本地时区?

解决方案

我想我想通了:计算自纪元以来的秒数，然后使用 time.localtime 转换为本地 timzeone，然后将时间结构转换回日期时间...

EPOCH_DATETIME = datetime.datetime(1970,1,1)SECONDS_PER_DAY = 24*60*60def utc_to_local_datetime(utc_datetime):delta = utc_datetime - EPOCH_DATETIMEutc_epoch = SECONDS_PER_DAY * delta.days + delta.secondstime_struct = time.localtime(utc_epoch)dt_args = time_struct[:6] + (delta.microseconds,)返回日期时间.日期时间( *dt_args )

它正确地应用了夏季/冬季 DST:

<预><代码>>>>utc_to_local_datetime( datetime.datetime(2010, 6, 6, 17, 29, 7, 730000) )datetime.datetime(2010, 6, 6, 19, 29, 7, 730000)>>>utc_to_local_datetime( datetime.datetime(2010, 12, 6, 17, 29, 7, 730000) )datetime.datetime(2010, 12, 6, 18, 29, 7, 730000)

I have a python datetime instance that was created using datetime.utcnow() and persisted in database.

For display, I would like to convert the datetime instance retrieved from the database to local datetime using the default local timezone (i.e., as if the datetime was created using datetime.now()).

How can I convert the UTC datetime to a local datetime using only python standard library (e.g., no pytz dependency)?

It seems one solution would be to use datetime.astimezone(tz), but how would you get the default local timezone?

解决方案

I think I figured it out: computes number of seconds since epoch, then converts to a local timzeone using time.localtime, and then converts the time struct back into a datetime...

EPOCH_DATETIME = datetime.datetime(1970,1,1)
SECONDS_PER_DAY = 24*60*60

def utc_to_local_datetime( utc_datetime ):
    delta = utc_datetime - EPOCH_DATETIME
    utc_epoch = SECONDS_PER_DAY * delta.days + delta.seconds
    time_struct = time.localtime( utc_epoch )
    dt_args = time_struct[:6] + (delta.microseconds,)
    return datetime.datetime( *dt_args )

It applies the summer/winter DST correctly:

>>> utc_to_local_datetime( datetime.datetime(2010, 6, 6, 17, 29, 7, 730000) )
datetime.datetime(2010, 6, 6, 19, 29, 7, 730000)
>>> utc_to_local_datetime( datetime.datetime(2010, 12, 6, 17, 29, 7, 730000) )
datetime.datetime(2010, 12, 6, 18, 29, 7, 730000)

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