Python logging: use milliseconds in time format

Please note Craig McDaniel's solution is preferable, unless you need support for all ISO 8601 format codes.

logging.Formatter's formatTime method looks like this:

def formatTime(self, record, datefmt=None): ct = self.converter(record.created) if datefmt: s = time.strftime(datefmt, ct) else: t = time.strftime("%Y-%m-%d %H:%M:%S", ct) s = "%s,%03d" % (t, record.msecs) return s 

Notice the comma in "%s,%03d". This can not be fixed by specifying a datefmt because ct is a time.struct_time and these objects do not record milliseconds.

If we change the definition of ct to make it a datetime object instead of a struct_time, then (at least with modern versions of Python) we can call ct.strftime and then we can use %f to format microseconds:

import logging import datetime as dt class MyFormatter(logging.Formatter): converter=dt.datetime.fromtimestamp def formatTime(self, record, datefmt=None): ct = self.converter(record.created) if datefmt: s = ct.strftime(datefmt) else: t = ct.strftime("%Y-%m-%d %H:%M:%S") s = "%s,%03d" % (t, record.msecs) return s logger = logging.getLogger(__name__) logger.setLevel(logging.DEBUG) console = logging.StreamHandler() logger.addHandler(console) formatter = MyFormatter(fmt='%(asctime)s %(message)s',datefmt='%Y-%m-%d,%H:%M:%S.%f') console.setFormatter(formatter) logger.debug('Jackdaws love my big sphinx of quartz.') # 2011-06-09,07:12:36.553554 Jackdaws love my big sphinx of quartz. 

Or, to get milliseconds, change the comma to a decimal point, and omit the datefmt argument:

class MyFormatter(logging.Formatter): converter=dt.datetime.fromtimestamp def formatTime(self, record, datefmt=None): ct = self.converter(record.created) if datefmt: s = ct.strftime(datefmt) else: t = ct.strftime("%Y-%m-%d %H:%M:%S") s = "%s.%03d" % (t, record.msecs) return s ... formatter = MyFormatter(fmt='%(asctime)s %(message)s') ... logger.debug('Jackdaws love my big sphinx of quartz.') # 2011-06-09 08:14:38.343 Jackdaws love my big sphinx of quartz. 

Adding msecs was the better option, Thanks. Here is my amendment using this with Python 3.5.3 in Blender

import logging logging.basicConfig(level=logging.DEBUG, format='%(asctime)s.%(msecs)03d %(levelname)s:\t%(message)s', datefmt='%Y-%m-%d %H:%M:%S' ) log = logging.getLogger(__name__) log.info("Logging Info") log.debug("Logging Debug") 

The simplest way I found was to override default_msec_format:

formatter = logging.Formatter('%(asctime)s') formatter.default_msec_format = '%s.%03d' 

I figured out a two-liner to get the Python logging module to output timestamps in RFC 3339 (ISO 1801 compliant) format, with both properly formatted milliseconds and timezone and without external dependencies:

import datetime import logging # Output timestamp, as the default format string does not include it logging.basicConfig(format="%(asctime)s: level=%(levelname)s module=%(module)s msg=%(message)s") # Produce RFC 3339 timestamps logging.Formatter.formatTime = (lambda self, record, datefmt=None: datetime.datetime.fromtimestamp(record.created, datetime.timezone.utc).astimezone().isoformat()) 

Example:

>>> logging.getLogger().error("Hello, world!") 2021-06-03T13:20:49.417084+02:00: level=ERROR module=<stdin> msg=Hello, world! 

Alternatively, that last line could be written out as follows:

def formatTime_RFC3339(self, record, datefmt=None): return ( datetime.datetime.fromtimestamp(record.created, datetime.timezone.utc) .astimezone() .isoformat() ) logging.Formatter.formatTime = formatTime_RFC3339 

That method could also be used on specific formatter instances, rather than overriding at the class level, in which case you will need to remove self from the method signature.

TLDR: Although it's not what the OP asked for, if you want to print all log timestamps as ISO8601 with milliseconds and UTC offset you can overwrite the default formatter formatTime like this:

import logging from datetime import datetime def formatTime(self, record, datefmt=None): return datetime.fromtimestamp(record.created).astimezone().isoformat(timespec='milliseconds') logging.Formatter.formatTime = formatTime 

produces logs like this

2024-01-15T19:23:01.371+01:00 INFO __main__ test 1 

The %(asctime)s is formatted through logging.Formatter.formatTime(self, record), the documentation states that formatTime will use time.strftime() which is not the same as datetime.strftime(). time.strftime has no way of printing milliseconds , datetime.strftime() on the other hand has %f. So you can't use %f on the datefmt.

If you only need to change the , (comma) to a . (dot) you have the simple options from other answers combining %(asctime)s, and %(msecs)03d like so (using logging.config.dictConfig() and a YAML file)

# log_config.yml version: 1 formatters: default: format: "%(asctime)s.%(msecs)03d %(levelname)-8s %(name)-15s %(message)s" datefmt: "%Y-%m-%d %H:%M:%S" 

But that will not work if you need to add the UTC offset /timezone after the milliseconds, for example.

In order to have a more sensible timestamp formatting you can implement your own formatter that subclasses logging.Formatter and just override formatTime. For example, the following formatter will produce logs with timestamps in ISO8601 including milliseconds and UTC offset by using datetime.isoformat():

# myformatter.py import logging from datetime import datetime class CustomFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): return datetime.fromtimestamp(record.created).astimezone().isoformat(timespec='milliseconds') 

In the code above

• record.created is the LogRecord attribute representing the number of seconds (float) since the epoch returned by time.time()
• datetime.fromtimestamp() is a class method that converts the epoch seconds to a datetime (naive)
• .astimezone() converts the naive datetime to timezone-aware datetime in the local timezone
• isoformat(): converts the timezone aware datetime to a ISO8601 string.

# log_config.yml version: 1 formatters: default: class: myformatter.CustomFormatter format: "%(asctime)s %(levelname)-8s %(name)-15s %(message)s" handlers: console: class: logging.StreamHandler stream: ext://sys.stdout formatter: default loggers: root: level: INFO handlers: [console] 

The above configuration results in :

2024-01-15T18:40:42.006307+01:00 INFO __main__ test 1 

where %(asctime)s value comes from CustomFormatter.formatTime()

Ultimately you can replace the logging.Formatter.formatTime with your own implementation instead of creating a new formatter:

import logging import logging.config import yaml from datetime import datetime def formatTime(self, record, datefmt=None): return datetime.fromtimestamp(record.created).astimezone().isoformat(timespec='milliseconds') logging.Formatter.formatTime = formatTime # no need for a custom formatter if we monkeypatch the default formatter with open("log_config.yml", "rt") as f: logging.config.dictConfig(yaml.safe_load(f.read())) logger = logging.getLogger(__name__) # __name__ myvar = 1 logger.info("test %s", myvar) 

Many outdated, over-complicated and weird answers here. The reason is that the documentation is inadequate and the simple solution is to just use basicConfig() and set it as follows:

logging.basicConfig(datefmt='%Y-%m-%d %H:%M:%S', format='{asctime}.{msecs:0<3.0f} {name} {threadName} {levelname}: {message}', style='{') 

The trick here was that you have to also set the datefmt argument, as the default messes it up and is not what is (currently) shown in the how-to python docs. So rather look here.

An alternative and possibly cleaner way, would have been to override the default_msec_format variable with:

formatter = logging.Formatter('%(asctime)s') formatter.default_msec_format = '%s.%03d' 

However, that did not work for unknown reasons.

_{PS. I am using Python 3.8.}

A simple expansion that doesn't require the datetime module and isn't handicapped like some other solutions is to use simple string replacement like so:

import logging import time class MyFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): ct = self.converter(record.created) if datefmt: if "%F" in datefmt: msec = "%03d" % record.msecs datefmt = datefmt.replace("%F", msec) s = time.strftime(datefmt, ct) else: t = time.strftime("%Y-%m-%d %H:%M:%S", ct) s = "%s,%03d" % (t, record.msecs) return s 

This way a date format can be written however you want, even allowing for region differences, by using %F for milliseconds. For example:

log = logging.getLogger(__name__) log.setLevel(logging.INFO) sh = logging.StreamHandler() log.addHandler(sh) fm = MyFormatter(fmt='%(asctime)s-%(levelname)s-%(message)s',datefmt='%H:%M:%S.%F') sh.setFormatter(fm) log.info("Foo, Bar, Baz") # 03:26:33.757-INFO-Foo, Bar, Baz 

After instantiating a Formatter I usually set formatter.converter = gmtime. So in order for @unutbu's answer to work in this case you'll need:

class MyFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): ct = self.converter(record.created) if datefmt: s = time.strftime(datefmt, ct) else: t = time.strftime("%Y-%m-%d %H:%M:%S", ct) s = "%s.%03d" % (t, record.msecs) return s 

All I needed to do was set default_msec_format attribute before creating the formatter.

logging.Formatter.default_msec_format = '%s.%03d' # Just add this line formatter = logging.Formatter('%(asctime)s %(levelname)s - %(message)s') 

If you are using arrow or if you don't mind using arrow. You can substitute python's time formatting for arrow's one.

import logging from arrow.arrow import Arrow class ArrowTimeFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): arrow_time = Arrow.fromtimestamp(record.created) if datefmt: arrow_time = arrow_time.format(datefmt) return str(arrow_time) logger = logging.getLogger(__name__) default_handler = logging.StreamHandler() default_handler.setFormatter(ArrowTimeFormatter( fmt='%(asctime)s', datefmt='YYYY-MM-DD HH:mm:ss.SSS' )) logger.setLevel(logging.DEBUG) logger.addHandler(default_handler) 

Now you can use all of arrow's time formatting in datefmt attribute.

If you prefer to use style='{', fmt="{asctime}.{msecs:0<3.0f}" will 0-pad your microseconds to three places for consistency.

After burning some of my precious time the below hack worked for me. I just updated my formatter in settings.py and added datefmt as %y/%b/%Y %H:%M:%S and appended the milliseconds to the asctime like this {asctime}.{msecs:0<3.0f}

E.G:

 'formatters': { 'verbose': { 'format': '[{asctime}.{msecs:0<3.0f}] {levelname} [{threadName:s}] {module} → {message}', 'datefmt': "%y/%b/%Y %H:%M:%S", 'style': '{', }, } 

Using this smart answer for the timezone and the chosen answer, you can construct the millisecond and timezone with your desired format:

import logging import time if __name__ == "__main__": tz = time.strftime('%z') logging.basicConfig( format=( "%(asctime)s.%(msecs)03d" + tz + " %(levelname)s " "%(pathname)s:%(lineno)d[%(threadName)s]: %(message)s" ), level=logging.DEBUG, datefmt="%Y-%m-%dT%H:%M:%S", ) logging.info("log example") 

Personally, I like to keep all the logs in UTC but also have this explicitly in the log as a datetime without a timezone is meaningless in a multizone application:

 logging.Formatter.converter = time.gmtime logging.basicConfig( format=( "%(asctime)s.%(msecs)03d+0000 %(levelname)s " "%(pathname)s:%(lineno)d[%(threadName)s]: %(message)s" ), level=logging.DEBUG, datefmt="%Y-%m-%dT%H:%M:%S", ) 

My take on this is the following:

class MicrosecondsFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): return super(MicroSecondsFormatter, self).formatTime(record, self.datefmt.replace('%f', str(datetime.fromtimestamp(record.created).microsecond).ljust(6, '0'))) logging.Formatter = MicrosecondsFormatter 

The above adds support for "%f" in the date format, and so one can continue using the logging module as usual, for example:

log_format = f'%(asctime)s %(levelname)-8s %(message)s' log_date_format = '%d/%m/%Y %H:%M:%S.%f %z' logging.basicConfig(stream=sys.stdout, format=log_format, datefmt=log_date_format, level=logging.INFO) 

To allow users to specify a datefmt that contains %f, you could create a custom Formatter and override the formatTime() method.

Because the override is using super() to get the default formatted time, this code doesn't change the default behaviour of the formatTime() method.

Note that the code will truncate %f to milliseconds, as opposed to microseconds.

The code below does the following -

1. Calls super() to get the formatted time.
2. Creates the milliseconds (msecs) to use in the formatted time, using record.msecs as the base.
3. Splits the formatted time using %f as the separator.
4. Joins the split formatted time on msecs.
5. Returns the formatted time (either original, or updated with milliseconds if appropriate).

import logging class CustomFormatter(logging.Formatter): def formatTime(self, record: logging.LogRecord, datefmt: str|None=None) -> str: '''Allow `datafmt` to interpret `%f` as milliseconds.''' s = super().formatTime(record, datefmt) if '%f' in s: s_split = s.split('%f') msecs = '%03d' % record.msecs s = msecs.join(s_split) return s fmt='%(asctime)s %(levelname)-8s => %(message)s' datefmt='%Y-%m-%d %H:%M:%S.%f' stdout_handler = logging.StreamHandler() stdout_handler.setFormatter(CustomFormatter(fmt, datefmt)) logger = logging.getLogger(__name__) logger.setLevel(logging.INFO) logger.addHandler(stdout_handler) logger.info('FooBar') 

tl;dr for folks looking here for an ISO formatted date:

instead of using something like '%Y-%m-%d %H:%M:%S.%03d%z', create your own class as @unutbu indicated. Here's one for iso date format:

import logging from time import gmtime, strftime class ISOFormatter(logging.Formatter): def formatTime(self, record, datefmt=None): t = strftime("%Y-%m-%dT%H:%M:%S", gmtime(record.created)) z = strftime("%z",gmtime(record.created)) s = "%s.%03d%s" % (t, record.msecs,z) return s logger = logging.getLogger(__name__) logger.setLevel(logging.DEBUG) console = logging.StreamHandler() logger.addHandler(console) formatter = ISOFormatter(fmt='%(asctime)s - %(module)s - %(levelname)s - %(message)s') console.setFormatter(formatter) logger.debug('Jackdaws love my big sphinx of quartz.') #2020-10-23T17:25:48.310-0800 - <stdin> - DEBUG - Jackdaws love my big sphinx of quartz.