How to add a custom loglevel to Python's logging facility

user_98525 0
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I'd like to have loglevel TRACE (5) for my application, as I don't think that debug() is sufficient. Additionally log(5, msg) isn't what I want. How can I add a custom loglevel to a Python logger?

I've a mylogger.py with the following content:

import logging

@property
def log(obj):
    myLogger = logging.getLogger(obj.__class__.__name__)
    return myLogger

In my code I use it in the following way:

class ExampleClass(object):
    from mylogger import log

    def __init__(self):
        '''The constructor with the logger'''
        self.log.debug("Init runs")

Now I'd like to call self.log.trace("foo bar")

Edit (Dec 8th 2016): I changed the accepted answer to pfa's which is, IMHO, an excellent solution based on the very good proposal from Eric S.

python-logging logging python
17 Answers

While we have already plenty of correct answers, the following is in my opinion more pythonic:

import logging

from functools import partial, partialmethod

logging.TRACE = 5
logging.addLevelName(logging.TRACE, 'TRACE')
logging.Logger.trace = partialmethod(logging.Logger.log, logging.TRACE)
logging.trace = partial(logging.log, logging.TRACE)

If you want to use mypy on your code, it is recommended to add # type: ignore to suppress warnings from adding attribute.

user_69507500

I think you'll have to subclass the Logger class and add a method called trace which basically calls Logger.log with a level lower than DEBUG. I haven't tried this but this is what the docs indicate.

user_2296020

based on pinned answer, i wrote a little method which automaticaly create new logging levels

def set_custom_logging_levels(config={}):
    """
        Assign custom levels for logging
            config: is a dict, like
            {
                'EVENT_NAME': EVENT_LEVEL_NUM,
            }
        EVENT_LEVEL_NUM can't be like already has logging module
        logging.DEBUG       = 10
        logging.INFO        = 20
        logging.WARNING     = 30
        logging.ERROR       = 40
        logging.CRITICAL    = 50
    """
    assert isinstance(config, dict), "Configuration must be a dict"

    def get_level_func(level_name, level_num):
        def _blank(self, message, *args, **kws):
            if self.isEnabledFor(level_num):
                # Yes, logger takes its '*args' as 'args'.
                self._log(level_num, message, args, **kws) 
        _blank.__name__ = level_name.lower()
        return _blank

    for level_name, level_num in config.items():
        logging.addLevelName(level_num, level_name.upper())
        setattr(logging.Logger, level_name.lower(), get_level_func(level_name, level_num))

config may smth like that:

new_log_levels = {
    # level_num is in logging.INFO section, that's why it 21, 22, etc..
    "FOO":      21,
    "BAR":      22,
}
user_109007140

Someone might wanna do, a root level custom logging; and avoid the usage of logging.get_logger(''):

import logging
from datetime import datetime
c_now=datetime.now()
logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] :: %(message)s",
    handlers=[
        logging.StreamHandler(),
        logging.FileHandler("../logs/log_file_{}-{}-{}-{}.log".format(c_now.year,c_now.month,c_now.day,c_now.hour))
    ]
)
DEBUG_LEVELV_NUM = 99 
logging.addLevelName(DEBUG_LEVELV_NUM, "CUSTOM")
def custom_level(message, *args, **kws):
    logging.Logger._log(logging.root,DEBUG_LEVELV_NUM, message, args, **kws) 
logging.custom_level = custom_level
# --- --- --- --- 
logging.custom_level("Waka")
user_136540270
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