How to convert a UTC datetime to a local datetime using only standard library?
I have a python datetime
instance that was created using datetime.utcnow()
and persisted in database.
For display, I would like to convert the datetime
instance retrieved from the database to local datetime
using the default local timezone (i.e., as if the datetime
was created using datetime.now()
).
How can I convert the UTC datetime
to a local datetime
using only python standard library (e.g., no pytz
dependency)?
It seems one solution would be to use datetime.astimezone(tz)
, but how would you get the default local timezone?
Solution 1:
In Python 3.3+:
from datetime import datetime, timezone
def utc_to_local(utc_dt):
return utc_dt.replace(tzinfo=timezone.utc).astimezone(tz=None)
In Python 2/3:
import calendar
from datetime import datetime, timedelta
def utc_to_local(utc_dt):
# get integer timestamp to avoid precision lost
timestamp = calendar.timegm(utc_dt.timetuple())
local_dt = datetime.fromtimestamp(timestamp)
assert utc_dt.resolution >= timedelta(microseconds=1)
return local_dt.replace(microsecond=utc_dt.microsecond)
Using pytz
(both Python 2/3):
import pytz
local_tz = pytz.timezone('Europe/Moscow') # use your local timezone name here
# NOTE: pytz.reference.LocalTimezone() would produce wrong result here
## You could use `tzlocal` module to get local timezone on Unix and Win32
# from tzlocal import get_localzone # $ pip install tzlocal
# # get local timezone
# local_tz = get_localzone()
def utc_to_local(utc_dt):
local_dt = utc_dt.replace(tzinfo=pytz.utc).astimezone(local_tz)
return local_tz.normalize(local_dt) # .normalize might be unnecessary
Example
def aslocaltimestr(utc_dt):
return utc_to_local(utc_dt).strftime('%Y-%m-%d %H:%M:%S.%f %Z%z')
print(aslocaltimestr(datetime(2010, 6, 6, 17, 29, 7, 730000)))
print(aslocaltimestr(datetime(2010, 12, 6, 17, 29, 7, 730000)))
print(aslocaltimestr(datetime.utcnow()))
Output
Python 3.32010-06-06 21:29:07.730000 MSD+0400
2010-12-06 20:29:07.730000 MSK+0300
2012-11-08 14:19:50.093745 MSK+0400
Python 2
2010-06-06 21:29:07.730000
2010-12-06 20:29:07.730000
2012-11-08 14:19:50.093911
pytz
2010-06-06 21:29:07.730000 MSD+0400
2010-12-06 20:29:07.730000 MSK+0300
2012-11-08 14:19:50.146917 MSK+0400
Note: it takes into account DST and the recent change of utc offset for MSK timezone.
I don't know whether non-pytz solutions work on Windows.
Solution 2:
Since Python 3.9 you can use the zoneinfo
module.
First lets get that time with utcnow()
:
>>> from datetime import datetime
>>> database_time = datetime.utcnow()
>>> database_time
datetime.datetime(2021, 9, 24, 4, 18, 27, 706532)
Then create the time zones:
>>> from zoneinfo import ZoneInfo
>>> utc = ZoneInfo('UTC')
>>> localtz = ZoneInfo('localtime')
Then convert. To convert between timezones, the datetime must know what timezone it is in, then we just use astimezone()
:
>>> utctime = database_time.replace(tzinfo=utc)
>>> localtime = utctime.astimezone(localtz)
>>> localtime
datetime.datetime(2021, 9, 24, 6, 18, 27, 706532, tzinfo=zoneinfo.ZoneInfo(key='localtime'))
For Python 3.6 to 3.8 you need the backports.zoneinfo module:
>>> try:
>>> from zoneinfo import ZoneInfo
>>> except ImportError:
>>> from backports.zoneinfo import ZoneInfo
The rest is the same.
For versions earlier than that need pytz
or dateutil
. datutil works similar to zoneinfo:
>>> from dateutil import tz
>>> utc = tz.gettz('UTC')
>>> localtz = tz.tzlocal()
The Conversion:
>>> utctime = now.replace(tzinfo=UTC)
>>> localtime = utctime.astimezone(localtz)
>>> localtime
datetime.datetime(2010, 12, 30, 15, 51, 22, 114668, tzinfo=tzlocal())
pytz
has a different interface which is a result of Python's time zone handling not handling ambigous times:
>>> import pytz
>>> utc = pytz.timezone('UTC')
# There is no local timezone support, you need to know your timezone
>>> localtz = pytz.timezone('Europe/Paris')
>>> utctime = utc.localize(database_time)
>>> localtime = localtz.normalize(utctime.astimezone(localtz))
>>> localtime