from dateutil.tz import tzlocal
localtimezone = tzlocal()
Internally, this is a class that uses time.timezone and time.altzone (switching based on time.daylight), but creates a suitable timezone object from that.
You use this instead of a pytz timezone.
The alternative is to read the currently configured timezone from the operating system instead, but this differs widely from OS to OS. On Mac OS X you need to read the output of systemsetup -gettimezone:
$ systemsetup -gettimezone
Time Zone: Europe/Copenhagen
On Debian and Ubuntu systems, you can read /etc/timezone:
$ cat /etc/timezone
Europe/Oslo
On RedHat and direved systems, you'll need to read it from /etc/sysconfig/clock:
$ grep ZONE /etc/sysconfig/clock
ZONE="Europe/Oslo"
tzlocal module returns pytz tzinfo's object corresponding to the local timezone:
import time
from datetime import datetime
import pytz # $ pip install pytz
from tzlocal import get_localzone # $ pip install tzlocal
# get local timezone
local_tz = get_localzone()
# test it
# utc_now, now = datetime.utcnow(), datetime.now()
ts = time.time()
utc_now, now = datetime.utcfromtimestamp(ts), datetime.fromtimestamp(ts)
local_now = utc_now.replace(tzinfo=pytz.utc).astimezone(local_tz) # utc -> local
assert local_now.replace(tzinfo=None) == now
It works even during daylight savings time transitions when local time may be ambiguous.
local_tz also works for past dates even if utc offset for the local timezone was different at the time. dateutil.tz.tzlocal()-based solution fails in this case e.g., in Europe/Moscow timezone (example from 2013):
dateutil returns wrong UTC+4 offset instead of the correct UTC+3 on 1970-01-01.
For those bumping into this in 2017dateutil.tz.tzlocal() is still broken. The above example works now because the current utf offset is UTC+3 in Moscow (that by accident is equal to the utc offset from 1970). To demonstrate the error we can choose a date when utc offset is UTC+4:
>>> import os, time
>>> os.environ['TZ'] = 'Europe/Moscow'
>>> time.tzset()
>>> from datetime import datetime
>>> from dateutil.tz import tzlocal
>>> from tzlocal import get_localzone
>>> dateutil_tz = tzlocal()
>>> tzlocal_tz = get_localzone()
>>> ts = datetime(2014, 6,1).timestamp() # get date in 2014 when gmtoff=14400 in Moscow
>>> datetime.fromtimestamp(ts, dateutil_tz)
datetime.datetime(2014, 5, 31, 23, 0, tzinfo=tzlocal())
>>> datetime.fromtimestamp(ts, tzlocal_tz)
datetime.datetime(2014, 6, 1, 0, 0, tzinfo=<DstTzInfo 'Europe/Moscow' MSK+4:00:00 STD>)
dateutil returns wrong UTC+3 offset instead of the correct UTC+4 on 2014-06-01.
i don't know if this is useful for you or not, but i think it answers your more general problem:
if you have a date that is in an ambiguous timezone, like CST, simple-date (python 3.2+ only, sorry) can automate the search, and allows you to do things like prefer certain countries.
note how, by specifying a country you reduce the range of possible values sufficiently to allow conversion to UTC.
it's implemented by doing a search over the timezones in PyTZ:
>>> SimpleDate('2013-07-04 18:53 CST', country='CN', debug=True)
...
PyTzFactory: Have country code CN
PyTzFactory: Country code CN has 5 timezones
PyTzFactory: Expanded country codes to 5 timezones
PyTzFactory: Expanding ('CST',)
PyTzFactory: Name lookup failed for CST
PyTzFactory: Found CST using Asia/Shanghai
PyTzFactory: Found CST using Asia/Harbin
PyTzFactory: Found CST using Asia/Chongqing
PyTzFactory: Found CST using Asia/Urumqi
PyTzFactory: Found CST using Asia/Kashgar
PyTzFactory: Expanded timezone to 5 timezones
PyTzFactory: New offset 8:00:00 for Asia/Shanghai
PyTzFactory: Known offset 8:00:00 for Asia/Harbin
PyTzFactory: Known offset 8:00:00 for Asia/Chongqing
PyTzFactory: Known offset 8:00:00 for Asia/Urumqi
PyTzFactory: Known offset 8:00:00 for Asia/Kashgar
PyTzFactory: Have 1 distinct timezone(s)
PyTzFactory: Found Asia/Shanghai
...
SimpleDate('2013-07-04 18:53 CST')
finally, to answer the question asked directly, it also wraps tzlocal, as mentioned in another answer here, so will automatically do what you expect if you don't give a timezone. for example, i live in chile, so
Since Python 3.6, you can simply run naive_datetime.astimezone() and system time zone will be added to naive_datetime object.
If called without arguments (or with tz=None) the system local timezone is assumed for the target timezone. The .tzinfo attribute of the converted datetime instance will be set to an instance of timezone with the zone name and offset obtained from the OS.