如果我将UTC时间增加1小时并进行本地化，或者将本地时间增加1小时，为什么会有所不同？ [英] Why does it make a difference if I add 1 hour to the UTC time and localize or 1 hour to the local time?

问题描述

from datetime import datetime, timezone, timedelta
import pytz

t11 = datetime(1918, 4, 15, 0, 0, tzinfo=timezone.utc).astimezone(pytz.timezone('Europe/Berlin'))
t12 = t11 + timedelta(hours=1)

t2 = datetime(1918, 4, 15, 1, 0, tzinfo=timezone.utc).astimezone(pytz.timezone('Europe/Berlin'))

print(t12)
print(t2)

已观察

Observed

1918-04-15 02:00:00+01:00
1918-04-15 03:00:00+02:00

期望

我期望两者都是我所看到的 t2 。关键的区别是 t2.hour 与 t12.hour 。对于可识别时区的datetime对象，我希望小时为本地小时。

Expected

I expected both to be what I see for t2. The crucial difference is t2.hour vs t12.hour. For a timezone-aware datetime object, I expected the hour to be the local hour.

如何更改此行为？这样的原因是什么？

How can I change this behaviour? What is the reason for having it like this?

推荐答案

我将不接受以下内容，因为它仅说明了操作方法对。它并不能解释为什么添加timedelta在一开始就无法按预期方式工作。

I will not accept the following, because it only explains how to do it right. It doesn't explain why adding timedelta doesn't work the expected way in the first place.

此答案建议采用以下方法：

from datetime import datetime, timezone, timedelta
import pytz

# Timezone-aware object to start with
t11 = datetime(1918, 4, 15, 0, 0, tzinfo=timezone.utc).astimezone(pytz.timezone('Europe/Berlin'))

# Extract timezone information
tzinfo = t11.tzinfo

# Convert to UTC, add timedelta, convert to local timezone
t13 = (t11.astimezone(pytz.timezone('utc')) + timedelta(hours=1)).astimezone(tzinfo)

另一种方法：

t14 = t11 + timedelta(hours=1)  # Invalid timezone!
t14 = t14.astimezone(pytz.utc).astimezone(t14.tzinfo)  # Fix the timezone

现在我有：

t11: 1918-04-15 01:00:00+01:00
t13: 1918-04-15 03:00:00+02:00  # one hour more and +1h because of DST

多一小时又+ 1h

摆锤

包 摆锤 是另一种解决方法：

Pendulum

The package pendulum is another way to fix it:

from pendulum import datetime
from datetime import timedelta
import pytz

t11 = datetime(1918, 4, 15, 0, 0).astimezone(pytz.timezone('Europe/Berlin'))
t12 = t11 + timedelta(hours=1)

t2 = datetime(1918, 4, 15, 1, 0).astimezone(pytz.timezone('Europe/Berlin'))

给予：

t11: 1918-04-15T01:00:00+01:00
t12: 1918-04-15T03:00:00+02:00
t2 : 1918-04-15T03:00:00+02:00

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