How do I use timezones with a datetime object in python?

Question

How do I properly represent a different timezone using the datetime module? The following example using myTimeZone() only works because I know that EDT is one hour ahead of me. What is the replacement for that commented part of the code?

import datetime, re
from datetime import tzinfo

class myTimeZone(tzinfo):
    """docstring for myTimeZone"""
    def utfoffset(self, dt):
        return timedelta(hours=1)
    
def myDateHandler(aDateString):
    """u'Sat,  6 Sep 2008 21:16:33 EDT'"""
    _my_date_pattern = re.compile(r'\w+\,\s+(\d+)\s+(\w+)\s+(\d+)\s+(\d+)\:(\d+)\:(\d+)')
    day, month, year, hour, minute, second = _my_date_pattern.search(aDateString).groups()
    month = [
            'JAN', 'FEB', 'MAR', 
            'APR', 'MAY', 'JUN', 
            'JUL', 'AUG', 'SEP', 
            'OCT', 'NOV', 'DEC'
    ].index(month.upper()) + 1
    dt = datetime.datetime(
        int(year), int(month), int(day), 
        int(hour), int(minute), int(second)
    )                   
    # dt = dt - datetime.timedelta(hours=1)
    # dt = dt - dt.tzinfo.utfoffset(myTimeZone())
    return (dt.year, dt.month, dt.day, dt.hour, dt.minute, dt.second, 0, 0, 0)

def main():
    print myDateHandler("Sat,  6 Sep 2008 21:16:33 EDT")

if __name__ == '__main__':
    main()

your specific date/time format can be handled using email.utils stdlib package: ts = mktime_tz(parsedate_tz('Sat, 6 Sep 2008 21:16:33 EDT')) — jfs
– jfs, Commented Jan 1, 2016 at 2:29

gerrit · Accepted Answer · 2014-07-30 19:25:10Z

39

I recommend babel and pytz when working with timezones. Keep your internal datetime objects naive and in UTC and convert to your timezone for formatting only. The reason why you probably want naive objects (objects without timezone information) is that many libraries and database adapters have no idea about timezones.

Babel
pytz

edited Jul 30, 2014 at 19:25

gerrit

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answered Sep 22, 2008 at 20:59

Armin Ronacher

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4 Comments

saeedgnu Over a year ago

Please update the Babel's link to babel.pocoo.org (as the old website says)

saeedgnu Over a year ago

Also notice that babel is on top of pytz

tadasajon Over a year ago

Isn't it a contradiction to say "naive and in UTC"

jfs Over a year ago

@JonCrowell: naive datetime object has no timezone information. You can interpret it as a time in any timezone (it is ambiguous in other words) including UTC e.g., you could treat 2008-09-22 20:59:00 as time in UTC (it is 2008-09-22 13:59:00 PDT-0700).

Thomas Wouters · Accepted Answer · 2008-09-22 20:46:08Z

11

The Python standard library doesn't contain timezone information, because unfortunately timezone data changes a lot faster than Python. You need a third-party module for this; the usual choice is pytz

answered Sep 22, 2008 at 20:46

Thomas Wouters

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4 Comments

Bradley Kreider Over a year ago

That doesn't explain why the standard library can't handle -500 though.

Prof. Falken Over a year ago

That's not a valid reason. The standard library could use resources on the platform it's running on if available and gracefully degrade if time zone history was not found.

jfs Over a year ago

@Prof.Falken: how would you gracefully degrade if the timezone info is not available (raise exceptions, return (possibly) wrong results, both)? btw, see PEP 431: Time zone support improvements

Prof. Falken Over a year ago

@J.F.Sebastian, I don't know. Exceptions come to mind but I am no Python expert. It just seems to me that things could be better than they are. PEP 431 looks like a good start to me.

Scrool · Accepted Answer · 2013-02-07 19:40:48Z

7

For the current local timezone, you can you use:

>>> import time
>>> offset = time.timezone if (time.localtime().tm_isdst == 0) else time.altzone
>>> offset / 60 / 60 * -1
-9

The value returned is in seconds West of UTC (with areas East of UTC getting a negative value). This is the opposite to how we'd actually like it, hence the * -1.

localtime().tm_isdst will be zero if daylight savings is currently not in effect (although this may not be correct if an area has recently changed their daylight savings law).

edited Feb 7, 2013 at 19:40

Scrool

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answered Dec 12, 2009 at 13:35

Carlos H Romano

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1 Comment

jfs Over a year ago

time.timezone and time.altzone is not enough in some cases

FObersteiner · Accepted Answer · 2020-12-07 11:26:58Z

Python >= 3.9

Python comes with zoneinfo as part of the standard lib. Example usage:

from datetime import datetime, timezone
from zoneinfo import ZoneInfo
UTC = datetime(2012,11,10,9,0,0, tzinfo=timezone.utc)

# convert to another tz with "astimezone":
eastern = UTC.astimezone(ZoneInfo("US/Eastern"))

# note that it is safe to use "replace",
# to get the same wall time in a different tz:
pacific = eastern.replace(tzinfo=ZoneInfo("US/Pacific"))

print(UTC.isoformat())
print(eastern.isoformat())
print(pacific.isoformat())

# 2012-11-10T09:00:00+00:00
# 2012-11-10T04:00:00-05:00
# 2012-11-10T04:00:00-08:00

Also note this section from the docs:

The zoneinfo module does not directly provide time zone data, and instead pulls time zone information from the system time zone database or the first-party PyPI package tzdata, if available.

So don't forget to call a pip install tzdata, on Windows at least.

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