我需要做什么

我有一个不了解时区的datetime对象,我需要向它添加一个时区,以便能够将它与其他了解时区的datetime对象进行比较。我不想将我的整个应用程序转换为不知道这个遗留情况的时区。

我的努力

首先,演示问题:

Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) 
[GCC 4.2.1 (Apple Inc. build 5646)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import datetime
>>> import pytz
>>> unaware = datetime.datetime(2011,8,15,8,15,12,0)
>>> unaware
datetime.datetime(2011, 8, 15, 8, 15, 12)
>>> aware = datetime.datetime(2011,8,15,8,15,12,0,pytz.UTC)
>>> aware
datetime.datetime(2011, 8, 15, 8, 15, 12, tzinfo=<UTC>)
>>> aware == unaware
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't compare offset-naive and offset-aware datetimes

首先,我尝试了astimezone:

>>> unaware.astimezone(pytz.UTC)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: astimezone() cannot be applied to a naive datetime
>>>

这个失败并不奇怪,因为它实际上是在尝试进行转换。Replace似乎是一个更好的选择(如如何在Python中获得“时区感知”的datetime.today()值?):

>>> unaware.replace(tzinfo=pytz.UTC)
datetime.datetime(2011, 8, 15, 8, 15, 12, tzinfo=<UTC>)
>>> unaware == aware
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't compare offset-naive and offset-aware datetimes
>>> 

但正如您所看到的,replace似乎设置了tzinfo,但并没有使对象感知。我准备在解析输入字符串之前修改输入字符串以获得时区(如果有问题的话,我将使用dateutil进行解析),但这似乎非常笨拙。

此外,我在Python 2.6和Python 2.7中都尝试了这一点,得到了相同的结果。

上下文

I am writing a parser for some data files. There is an old format I need to support where the date string does not have a timezone indicator. I've already fixed the data source, but I still need to support the legacy data format. A one time conversion of the legacy data is not an option for various business BS reasons. While in general, I do not like the idea of hard-coding a default timezone, in this case it seems like the best option. I know with reasonable confidence that all the legacy data in question is in UTC, so I'm prepared to accept the risk of defaulting to that in this case.


当前回答

在时区之间更改

import pytz
from datetime import datetime

other_tz = pytz.timezone('Europe/Madrid')

# From random aware datetime...
aware_datetime = datetime.utcnow().astimezone(other_tz)
>> 2020-05-21 08:28:26.984948+02:00

# 1. Change aware datetime to UTC and remove tzinfo to obtain an unaware datetime
unaware_datetime = aware_datetime.astimezone(pytz.UTC).replace(tzinfo=None)
>> 2020-05-21 06:28:26.984948

# 2. Set tzinfo to UTC directly on an unaware datetime to obtain an utc aware datetime
aware_datetime_utc = unaware_datetime.replace(tzinfo=pytz.UTC)
>> 2020-05-21 06:28:26.984948+00:00

# 3. Convert the aware utc datetime into another timezone
reconverted_aware_datetime = aware_datetime_utc.astimezone(other_tz)
>> 2020-05-21 08:28:26.984948+02:00

# Initial Aware Datetime and Reconverted Aware Datetime are equal
print(aware_datetime1 == aware_datetime2)
>> True

其他回答

对于那些只是想使一个时区感知datetime

import datetime

datetime.datetime(2019, 12, 7, tzinfo=datetime.timezone.utc)

对于那些在python 3.9 stdlib中希望使用非utc时区的datetime的人

import datetime
from zoneinfo import ZoneInfo

datetime.datetime(2019, 12, 7, tzinfo=ZoneInfo("America/Los_Angeles")) 

Python 3.9添加了zoneinfo模块,所以现在只需要标准库!

from zoneinfo import ZoneInfo
from datetime import datetime
unaware = datetime(2020, 10, 31, 12)

附加一个时区:

>>> unaware.replace(tzinfo=ZoneInfo('Asia/Tokyo'))
datetime.datetime(2020, 10, 31, 12, 0, tzinfo=zoneinfo.ZoneInfo(key='Asia/Tokyo'))
>>> str(_)
'2020-10-31 12:00:00+09:00'

附加系统的本地时区:

>>> unaware.replace(tzinfo=ZoneInfo('localtime'))
datetime.datetime(2020, 10, 31, 12, 0, tzinfo=zoneinfo.ZoneInfo(key='localtime'))
>>> str(_)
'2020-10-31 12:00:00+01:00'

随后,它被正确地转换为其他时区:

>>> unaware.replace(tzinfo=ZoneInfo('localtime')).astimezone(ZoneInfo('Asia/Tokyo'))
datetime.datetime(2020, 10, 31, 20, 0, tzinfo=backports.zoneinfo.ZoneInfo(key='Asia/Tokyo'))
>>> str(_)
'2020-10-31 20:00:00+09:00'

可用时区的维基百科列表


Windows没有系统时区数据库,所以这里需要一个额外的包:

pip install tzdata  

在Python 3.6到3.8中,有一个允许使用zoneinfo的后端口:

pip install backports.zoneinfo

然后:

from backports.zoneinfo import ZoneInfo

我在Django中使用这个语句将一个无意识的时间转换为一个有意识的时间:

from django.utils import timezone

dt_aware = timezone.make_aware(dt_unaware, timezone.get_current_timezone())

这是@Sérgio和@unutbu的答案。它将“只是工作”与任何一个pytz。对象或IANA时区字符串。

def make_tz_aware(dt, tz='UTC', is_dst=None):
    """Add timezone information to a datetime object, only if it is naive."""
    tz = dt.tzinfo or tz
    try:
        tz = pytz.timezone(tz)
    except AttributeError:
        pass
    return tz.localize(dt, is_dst=is_dst) 

这似乎是datetime. localalize()(或.inform()或. aware())应该做的事情,为tz参数接受字符串和时区对象,如果没有指定时区,则默认为UTC。

所有这些例子都使用了一个外部模块,但你可以只使用datetime模块来实现相同的结果,正如下面的SO答案所示:

from datetime import datetime, timezone

dt = datetime.now()
dt = dt.replace(tzinfo=timezone.utc)

print(dt.isoformat())
# '2017-01-12T22:11:31+00:00'

更少的依赖,没有pytz问题。

注意:如果你想在python3和python2中使用它,你也可以在时区导入中使用它(为UTC硬编码):

try:
    from datetime import timezone
    utc = timezone.utc
except ImportError:
    #Hi there python2 user
    class UTC(tzinfo):
        def utcoffset(self, dt):
            return timedelta(0)
        def tzname(self, dt):
            return "UTC"
        def dst(self, dt):
            return timedelta(0)
    utc = UTC()