Question

I’m having an issue creating dates in python, as the dates I create are not respecting daylight savings time in some scenarios.

For example, if I go to my shell and run

>>> adjust_datetime_to_timezone(value=datetime.datetime.now(), from_tz=timezone('UTC'), to_tz=timezone('US/Pacific'))
datetime.datetime(2011, 7, 7, 12, 41, 16, 337918, tzinfo=<DstTzInfo 'US/Pacific' PDT-1 day, 17:00:00 DST>)

I get the correct time.

I want to create a date that is the start of the current date, so I run:

>>> datetime.datetime(year=2011, month=7, day=7,  tzinfo=timezone('US/Pacific'))
datetime.datetime(2011, 7, 7, 0, 0, tzinfo=<DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD>)

Note that is a PST date, because when I convert it to UTC:

>>> adjust_datetime_to_timezone(datetime.datetime(year=2011, month=7, day=7,  tzinfo=timezone('US/Pacific')), from_tz=timezone('US/Pacific'), to_tz=timezone('UTC')) datetime.datetime(2011, 7, 7, 8, 0, tzinfo=<UTC>)

Note that’s 07/07/2011 08:00 AM UTC which is actually 01:00 AM PDT.

Anyone know why python would be giving me PST dates for the datetime.datetime constructor but not for adjust_datetime_to_timezone?

Answer 1

Since I see <DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD>, it appears you are using pytz. In that case, you can use the localize method to create timezone-aware datetimes that are adjusted for Daylight Savings Time. (Avoid using datetime.datetime‘s tzinfo argument since it does not adjust for Daylight Savings Time.)

import pytz
import datetime as dt

now=dt.datetime(year=2011, month=7, day=7)
utc=pytz.utc
pacific=pytz.timezone('US/Pacific')    
now_pacific=pacific.localize(now)    
now_utc=now_pacific.astimezone(utc)

print(repr(now_pacific))
# datetime.datetime(2011, 7, 7, 0, 0, tzinfo=<DstTzInfo 'US/Pacific' PDT-1 day, 17:00:00 DST>)
print(repr(now_utc))
# datetime.datetime(2011, 7, 7, 7, 0, tzinfo=<UTC>)