How to Change the time zone in Python logging?

Question

I would like to change the timestamp in the log file so that it reflects my current time zone so that i can debug errors at a faster rate,

is it possible that i can change the time zone in the log file ?

currently my config is:

logging.basicConfig(filename='audit.log',
                filemode='w',
                level=logging.INFO,
                format='%(asctime)s %(message)s',
                datefmt='%m/%d/%Y %I:%M:%S %p')

Answer 1

How to log the timezone

%Z from strftime format

Windows

>>> import logging
>>> logging.basicConfig(format="%(asctime)s %(message)s", datefmt="%m/%d/%Y %I:%M:%S %p %Z")
>>> logging.error('test')
11/03/2017 02:29:54 PM Mountain Daylight Time test

Linux

>>> import logging
>>> logging.basicConfig(format="%(asctime)s %(message)s", datefmt="%m/%d/%Y %I:%M:%S %p %Z")
>>> logging.error('test')
11/03/2017 02:30:50 PM MDT test

If the question is

How do I log in a different timezone than the local time on the server?

part of the answer is logging.Formatter.converter, however, you have to understand naive and aware datetime objects. Unless you want to write your own timezone module, I highly suggest the pytz library (pip install pytz). Python 3 includes a UTC and UTC offset timezone, but there's rules you'll have to implement for daylight saving or other offsets, so I would suggest the pytz library, even for python 3.

For example,

>>> import datetime
>>> utc_now = datetime.datetime.utcnow()
>>> utc_now.isoformat()
'2019-05-21T02:30:09.422638'
>>> utc_now.tzinfo
(None)

If I apply a timezone to this datetime object, the time won't change (or will issue a ValueError for < python 3.7ish).

>>> mst_now = utc_now.astimezone(pytz.timezone('America/Denver'))
>>> mst_now.isoformat()
'2019-05-21T02:30:09.422638-06:00'
>>> utc_now.isoformat()
'2019-05-21T02:30:09.422638'

However, if instead, I do

>>> import pytz
>>> utc_now = datetime.datetime.now(tz=pytz.timezone('UTC'))
>>> utc_now.tzinfo
<UTC>

now we can create a properly translated datetime object in whatever timezone we wish

>>> mst_now = utc_now.astimezone(pytz.timezone('America/Denver'))
>>> mst_now.isoformat()
'2019-05-20T20:31:44.913939-06:00'

Aha! Now to apply this to the logging module.

Epoch timestamp to string representation with timezone

The LogRecord.created attribute is set to the time when the LogRecord was created (as returned by time.time()), from the time module. This returns a timestamp (seconds since the epoch). You can do your own translation to a given timezone, but again, I suggest pytz, by overriding the converter.

import datetime
import logging
import pytz

class Formatter(logging.Formatter):
    """override logging.Formatter to use an aware datetime object"""
    def converter(self, timestamp):
        dt = datetime.datetime.fromtimestamp(timestamp)
        tzinfo = pytz.timezone('America/Denver')
        return tzinfo.localize(dt)
        
    def formatTime(self, record, datefmt=None):
        dt = self.converter(record.created)
        if datefmt:
            s = dt.strftime(datefmt)
        else:
            try:
                s = dt.isoformat(timespec='milliseconds')
            except TypeError:
                s = dt.isoformat()
        return s

Python 3.5, 2.7

>>> logger = logging.root
>>> handler = logging.StreamHandler()
>>> handler.setFormatter(Formatter("%(asctime)s %(message)s"))
>>> logger.addHandler(handler)
>>> logger.setLevel(logging.DEBUG)
>>> logger.debug('test')
2019-05-20T22:25:10.758782-06:00 test

Python 3.7

>>> logger = logging.root
>>> handler = logging.StreamHandler()
>>> handler.setFormatter(Formatter("%(asctime)s %(message)s"))
>>> logger.addHandler(handler)
>>> logger.setLevel(logging.DEBUG)
>>> logger.debug('test')
2019-05-20T22:29:21.678-06:00 test

Substitute America/Denver with America/Anchorage for the posix timezone as defined by pytz

>>> next(_ for _ in pytz.common_timezones if 'Alaska' in _)
'US/Alaska'

US/Alaska is deprecated

>>> [_ for _ in pytz.all_timezones if 'Anchorage' in _]
['America/Anchorage']

Local

If you got to this question and answers looking for how to log the local timezone, then instead of hardcoding the timezone, get tzlocal (pip install tzlocal) and replace

        tzinfo = pytz.timezone('America/Denver')

with

        tzinfo = tzlocal.get_localzone()

Now it will work on whatever server runs the script, with the timezone on the server.

Caveat when not logging UTC

I should add, depending on the application, logging in local time zones can create ambiguity or at least confusion twice a year, where 2 AM is skipped or 1 AM repeats, and possibly others.