Calculating timedeltas across daylight saving

Question

I’m facing a python timezones problem and am unsure of what is the right approach to deal with it. I have to calculate timedeltas from given start and end DateTime objects. It can happen that daylight saving time will change during the runtime of my events, so I have to take that into account.

So far I’ve learned that for this to work I need to save my start and end times as timezone aware DateTime objects rather than regular UTC DateTimes.

I’ve been looking into DateTime.tzinfo, pytz,and dateutil but from what I understand these are all mostly focused on localised display of UTC DateTime objects or calculating the offsets between different timezones. Other helpers I found expect the timezone as a UTC offset, so would already require me to know if a date is affected by daylight saving or not.

So, I guess my question is: Is there a way so save a DateTime as "Central Europe" and have it be aware of daytime savings when doing calculations with them? Or, if not, what would be the established way to check if two DateTime objects are within daylight saving, so I can manually adjust the result if necessary?

I’d be grateful for any pointers.

Asked By: Overgrown

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Answer 1

You just need to produce an aware (localised) datetime instance, then any calculation you do with it will take DST into account. Here as an example with pytz:

>>> import pytz
>>> from datetime import *
>>> berlin = pytz.timezone('Europe/Berlin')
>>> d1 = berlin.localize(datetime(2023, 3, 25, 12))
datetime.datetime(2023, 3, 25, 12, 0, tzinfo=<DstTzInfo 'Europe/Berlin' CET+1:00:00 STD>)
>>> d2 = berlin.localize(datetime(2023, 3, 26, 12))
datetime.datetime(2023, 3, 26, 12, 0, tzinfo=<DstTzInfo 'Europe/Berlin' CEST+2:00:00 DST>)
>>> d2 - d1
datetime.timedelta(seconds=82800)
>>> (d2 - d1).total_seconds() / 60 / 60
23.0

Answered By: deceze

Calculating timedeltas across daylight saving

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