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.
To people reading in 2022 and beyond: you should probably check out the currently next-highest-rated answer here: https://stackoverflow.com/a/35804945/1691778
My original answer is below.
--
#Eric S.
Eric S.'s answer is excellent, but I learned by experimentation that this will always cause messages logged at the new debug level to be printed -- regardless of what the log level is set to. So if you make a new level number of 9, if you call setLevel(50), the lower level messages will erroneously be printed.
To prevent that from happening, you need another line inside the "debugv" function to check if the logging level in question is actually enabled.
Fixed example that checks if the logging level is enabled:
import logging
DEBUG_LEVELV_NUM = 9
logging.addLevelName(DEBUG_LEVELV_NUM, "DEBUGV")
def debugv(self, message, *args, **kws):
if self.isEnabledFor(DEBUG_LEVELV_NUM):
# Yes, logger takes its '*args' as 'args'.
self._log(DEBUG_LEVELV_NUM, message, args, **kws)
logging.Logger.debugv = debugv
If you look at the code for class Logger in logging.__init__.py for Python 2.7, this is what all the standard log functions do (.critical, .debug, etc.).
I apparently can't post replies to others' answers for lack of reputation... hopefully Eric will update his post if he sees this. =)
Combining all of the existing answers with a bunch of usage experience, I think that I have come up with a list of all the things that need to be done to ensure completely seamless usage of the new level. The steps below assume that you are adding a new level TRACE with value logging.DEBUG - 5 == 5:
logging.addLevelName(logging.DEBUG - 5, 'TRACE') needs to be invoked to get the new level registered internally so that it can be referenced by name.
The new level needs to be added as an attribute to logging itself for consistency: logging.TRACE = logging.DEBUG - 5.
A method called trace needs to be added to the logging module. It should behave just like debug, info, etc.
A method called trace needs to be added to the currently configured logger class. Since this is not 100% guaranteed to be logging.Logger, use logging.getLoggerClass() instead.
All the steps are illustrated in the method below:
def addLoggingLevel(levelName, levelNum, methodName=None):
"""
Comprehensively adds a new logging level to the `logging` module and the
currently configured logging class.
`levelName` becomes an attribute of the `logging` module with the value
`levelNum`. `methodName` becomes a convenience method for both `logging`
itself and the class returned by `logging.getLoggerClass()` (usually just
`logging.Logger`). If `methodName` is not specified, `levelName.lower()` is
used.
To avoid accidental clobberings of existing attributes, this method will
raise an `AttributeError` if the level name is already an attribute of the
`logging` module or if the method name is already present
Example
-------
>>> addLoggingLevel('TRACE', logging.DEBUG - 5)
>>> logging.getLogger(__name__).setLevel("TRACE")
>>> logging.getLogger(__name__).trace('that worked')
>>> logging.trace('so did this')
>>> logging.TRACE
5
"""
if not methodName:
methodName = levelName.lower()
if hasattr(logging, levelName):
raise AttributeError('{} already defined in logging module'.format(levelName))
if hasattr(logging, methodName):
raise AttributeError('{} already defined in logging module'.format(methodName))
if hasattr(logging.getLoggerClass(), methodName):
raise AttributeError('{} already defined in logger class'.format(methodName))
# This method was inspired by the answers to Stack Overflow post
# http://stackoverflow.com/q/2183233/2988730, especially
# http://stackoverflow.com/a/13638084/2988730
def logForLevel(self, message, *args, **kwargs):
if self.isEnabledFor(levelNum):
self._log(levelNum, message, args, **kwargs)
def logToRoot(message, *args, **kwargs):
logging.log(levelNum, message, *args, **kwargs)
logging.addLevelName(levelNum, levelName)
setattr(logging, levelName, levelNum)
setattr(logging.getLoggerClass(), methodName, logForLevel)
setattr(logging, methodName, logToRoot)
You can find an even more detailed implementation in the utility library I maintain, haggis. The function haggis.logs.add_logging_level is a more production-ready implementation of this answer.
I took the avoid seeing "lambda" answer and had to modify where the log_at_my_log_level was being added. I too saw the problem that Paul did – I don't think this works. Don't you need logger as the first arg in log_at_my_log_level? This worked for me
import logging
DEBUG_LEVELV_NUM = 9
logging.addLevelName(DEBUG_LEVELV_NUM, "DEBUGV")
def debugv(self, message, *args, **kws):
# Yes, logger takes its '*args' as 'args'.
self._log(DEBUG_LEVELV_NUM, message, args, **kws)
logging.Logger.debugv = debugv
This question is rather old, but I just dealt with the same topic and found a way similiar to those already mentioned which appears a little cleaner to me. This was tested on 3.4, so I'm not sure whether the methods used exist in older versions:
from logging import getLoggerClass, addLevelName, setLoggerClass, NOTSET
VERBOSE = 5
class MyLogger(getLoggerClass()):
def __init__(self, name, level=NOTSET):
super().__init__(name, level)
addLevelName(VERBOSE, "VERBOSE")
def verbose(self, msg, *args, **kwargs):
if self.isEnabledFor(VERBOSE):
self._log(VERBOSE, msg, args, **kwargs)
setLoggerClass(MyLogger)
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.
Who started the bad practice of using internal methods (self._log) and why is each answer based on that?! The pythonic solution would be to use self.log instead so you don't have to mess with any internal stuff:
import logging
SUBDEBUG = 5
logging.addLevelName(SUBDEBUG, 'SUBDEBUG')
def subdebug(self, message, *args, **kws):
self.log(SUBDEBUG, message, *args, **kws)
logging.Logger.subdebug = subdebug
logging.basicConfig()
l = logging.getLogger()
l.setLevel(SUBDEBUG)
l.subdebug('test')
l.setLevel(logging.DEBUG)
l.subdebug('test')
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.
I find it easier to create a new attribute for the logger object that passes the log() function. I think the logger module provides the addLevelName() and the log() for this very reason. Thus no subclasses or new method needed.
import logging
#property
def log(obj):
logging.addLevelName(5, 'TRACE')
myLogger = logging.getLogger(obj.__class__.__name__)
setattr(myLogger, 'trace', lambda *args: myLogger.log(5, *args))
return myLogger
now
mylogger.trace('This is a trace message')
should work as expected.
Tips for creating a custom logger:
Do not use _log, use log (you don't have to check isEnabledFor)
the logging module should be the one creating instance of the custom logger since it does some magic in getLogger, so you will need to set the class via setLoggerClass
You do not need to define __init__ for the logger, class if you are not storing anything
# Lower than debug which is 10
TRACE = 5
class MyLogger(logging.Logger):
def trace(self, msg, *args, **kwargs):
self.log(TRACE, msg, *args, **kwargs)
When calling this logger use setLoggerClass(MyLogger) to make this the default logger from getLogger
logging.setLoggerClass(MyLogger)
log = logging.getLogger(__name__)
# ...
log.trace("something specific")
You will need to setFormatter, setHandler, and setLevel(TRACE) on the handler and on the log itself to actually se this low level trace
This worked for me:
import logging
logging.basicConfig(
format=' %(levelname)-8.8s %(funcName)s: %(message)s',
)
logging.NOTE = 32 # positive yet important
logging.addLevelName(logging.NOTE, 'NOTE') # new level
logging.addLevelName(logging.CRITICAL, 'FATAL') # rename existing
log = logging.getLogger(__name__)
log.note = lambda msg, *args: log._log(logging.NOTE, msg, args)
log.note('school\'s out for summer! %s', 'dude')
log.fatal('file not found.')
The lambda/funcName issue is fixed with logger._log as #marqueed pointed out. I think using lambda looks a bit cleaner, but the drawback is that it can't take keyword arguments. I've never used that myself, so no biggie.
NOTE setup: school's out for summer! dude
FATAL setup: file not found.
As alternative to adding an extra method to the Logger class I would recommend using the Logger.log(level, msg) method.
import logging
TRACE = 5
logging.addLevelName(TRACE, 'TRACE')
FORMAT = '%(levelname)s:%(name)s:%(lineno)d:%(message)s'
logging.basicConfig(format=FORMAT)
l = logging.getLogger()
l.setLevel(TRACE)
l.log(TRACE, 'trace message')
l.setLevel(logging.DEBUG)
l.log(TRACE, 'disabled trace message')
In my experience, this is the full solution the the op's problem... to avoid seeing "lambda" as the function in which the message is emitted, go deeper:
MY_LEVEL_NUM = 25
logging.addLevelName(MY_LEVEL_NUM, "MY_LEVEL_NAME")
def log_at_my_log_level(self, message, *args, **kws):
# Yes, logger takes its '*args' as 'args'.
self._log(MY_LEVEL_NUM, message, args, **kws)
logger.log_at_my_log_level = log_at_my_log_level
I've never tried working with a standalone logger class, but I think the basic idea is the same (use _log).
Addition to Mad Physicists example to get file name and line number correct:
def logToRoot(message, *args, **kwargs):
if logging.root.isEnabledFor(levelNum):
logging.root._log(levelNum, message, args, **kwargs)
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,
}
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")
I'm confused; with python 3.5, at least, it just works:
import logging
TRACE = 5
"""more detail than debug"""
logging.basicConfig()
logging.addLevelName(TRACE,"TRACE")
logger = logging.getLogger('')
logger.debug("n")
logger.setLevel(logging.DEBUG)
logger.debug("y1")
logger.log(TRACE,"n")
logger.setLevel(TRACE)
logger.log(TRACE,"y2")
output:
DEBUG:root:y1
TRACE:root:y2
Following up on the top-rated answers by Eric S. and Mad Physicist:
Fixed example that checks if the logging level is enabled:
import logging
DEBUG_LEVELV_NUM = 9
logging.addLevelName(DEBUG_LEVELV_NUM, "DEBUGV")
def debugv(self, message, *args, **kws):
if self.isEnabledFor(DEBUG_LEVELV_NUM):
# Yes, logger takes its '*args' as 'args'.
self._log(DEBUG_LEVELV_NUM, message, args, **kws)
logging.Logger.debugv = debugv
This code-snippet
adds a new log-level "DEBUGV" and assigns a number 9
defines a debugv-method, which logs a message with level "DEBUGV" unless the log-level is set to a value higher than 9 (e.g. log-level "DEBUG")
monkey-patches the logging.Logger-class, so that you can call logger.debugv
The suggested implementation worked well for me, but
code completion doesn't recognise the logger.debugv-method
pyright, which is part of our CI-pipeline, fails, because it cannot trace the debugv-member method of the Logger-class (see https://github.com/microsoft/pylance-release/issues/2335 about dynamically adding member-methods)
I ended up using inheritance as was suggested in Noufal Ibrahim's answer in this thread:
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.
Implementing Noufal Ibrahim's suggestion worked and pyright is happy:
import logging
# add log-level DEBUGV
DEBUGV = 9 # slightly lower than DEBUG (10)
logging.addLevelName(DEBUGV, "DEBUGV")
class MyLogger(logging.Logger):
"""Inherit from standard Logger and add level DEBUGV."""
def debugv(self, msg, *args, **kwargs):
"""Log 'msg % args' with severity 'DEBUGV'."""
if self.isEnabledFor(DEBUGV):
self._log(DEBUGV, msg, args, **kwargs)
logging.setLoggerClass(MyLogger)
Next you can initialise an instance of the extended logger using the logger-manager:
logger = logging.getLogger("whatever_logger_name")
Edit: In order to make pyright recognise the debugv-method, you may need to cast the logger returned by logging.getLogger, which would like this:
import logging
from typing import cast
logger = cast(MyLogger, logging.getLogger("whatever_logger_name"))
In case anyone wants an automated way to add a new logging level to the logging module (or a copy of it) dynamically, I have created this function, expanding #pfa's answer:
def add_level(log_name,custom_log_module=None,log_num=None,
log_call=None,
lower_than=None, higher_than=None, same_as=None,
verbose=True):
'''
Function to dynamically add a new log level to a given custom logging module.
<custom_log_module>: the logging module. If not provided, then a copy of
<logging> module is used
<log_name>: the logging level name
<log_num>: the logging level num. If not provided, then function checks
<lower_than>,<higher_than> and <same_as>, at the order mentioned.
One of those three parameters must hold a string of an already existent
logging level name.
In case a level is overwritten and <verbose> is True, then a message in WARNING
level of the custom logging module is established.
'''
if custom_log_module is None:
import imp
custom_log_module = imp.load_module('custom_log_module',
*imp.find_module('logging'))
log_name = log_name.upper()
def cust_log(par, message, *args, **kws):
# Yes, logger takes its '*args' as 'args'.
if par.isEnabledFor(log_num):
par._log(log_num, message, args, **kws)
available_level_nums = [key for key in custom_log_module._levelNames
if isinstance(key,int)]
available_levels = {key:custom_log_module._levelNames[key]
for key in custom_log_module._levelNames
if isinstance(key,str)}
if log_num is None:
try:
if lower_than is not None:
log_num = available_levels[lower_than]-1
elif higher_than is not None:
log_num = available_levels[higher_than]+1
elif same_as is not None:
log_num = available_levels[higher_than]
else:
raise Exception('Infomation about the '+
'log_num should be provided')
except KeyError:
raise Exception('Non existent logging level name')
if log_num in available_level_nums and verbose:
custom_log_module.warn('Changing ' +
custom_log_module._levelNames[log_num] +
' to '+log_name)
custom_log_module.addLevelName(log_num, log_name)
if log_call is None:
log_call = log_name.lower()
setattr(custom_log_module.Logger, log_call, cust_log)
return custom_log_module
I have a formatter that expects special attribute in the record, "user_id", that not always there(sometimes I add it to records using special logging.Filter).
I tried to override the makeRecord method of logging.Logger like so:
import logging
logging.basicConfig(level=logging.DEBUG,
format='%(asctime)-15s user_id=%(user_id)s %(filename)s:%(lineno)-15s: %(message)s')
class OneTestLogger(logging.Logger):
def makeRecord(self, name, level, fn, lno, msg, args, exc_info, func=None, extra=None):
rv = logging.Logger.makeRecord(self, name, level, fn, lno,
msg, args, exc_info,
func, extra)
rv.__dict__.setdefault('user_id', 'master')
return rv
if __name__ == '__main__':
logger = OneTestLogger('main')
print logger
logger.info('Starting test')
But that doesn't seem to work and I keep getting:
<main.MyLogger instance at 0x7f31a6a5b638>
No handlers could be found for logger "main"
What am I doing wrong?
Thanks.
Following the guideline provided in Logging Cookbook. Just the first part, I did not implement Filter (which does not appear in the below quote either).
This has usually meant that if you need to do anything special with a LogRecord, you’ve had to do one of the following.
Create your own Logger subclass, which overrides Logger.makeRecord(), and set it using setLoggerClass() before any loggers that you care about are instantiated.
I have simplifed your exampled just to add the 'hostname':
import logging
from socket import gethostname
logging.basicConfig(level=logging.DEBUG,
format='%(asctime)s - %(hostname)s - %(message)s')
class NewLogger(logging.Logger):
def makeRecord(self, *args, **kwargs):
rv = super(NewLogger, self).makeRecord(*args, **kwargs)
# updating the rv value of the original makeRecord
# my idea is to use the same logic than a decorator by
# intercepting the value return by the original makeRecord
# and expanded with what I need
rv.__dict__['hostname'] = gethostname()
# by curiosity I am checking what is in this dictionary
# print(rv.__dict__)
return rv
logging.setLoggerClass(NewLogger)
logger = logging.getLogger(__name__)
logger.info('Hello World!')
Note that this code worked on python 2.7
I've built custom exceptions that accept a parameter(s) and format their own message from constants. They also print to stdout so the user understands the issue.
For instance:
defs.py:
PATH_NOT_FOUND_ERROR = 'Cannot find path "{}"'
exceptions.py:
class PathNotFound(BaseCustomException):
"""Specified path was not found."""
def __init__(self, path):
msg = PATH_NOT_FOUND_ERROR.format(path)
print(msg)
super(PathNotFound, self).__init__(msg)
some_module.py
raise PathNotFound(some_invalid_path)
I also want to log the exceptions as they are thrown, the simplest way would be:
logger.debug('path {} not found'.format(some_invalid_path)
raise PathNotFound(some_invalid_path)
But doing this all across the code seems redundant, and especially it makes the constants pointless because if I decide the change the wording I need to change the logger wording too.
I've trying to do something like moving the logger to the exception class but makes me lose the relevant LogRecord properties like name, module, filename, lineno, etc. This approach also loses exc_info
Is there a way to log the exception and keeping the metadata without logging before raising every time?
If anyone's interested, here's a working solution
The idea was to find the raiser's frame and extract the relevant information from there.
Also had to override logging.makeRecord to let me override internal LogRecord attributes
Set up logging
class MyLogger(logging.Logger):
"""Custom Logger."""
def makeRecord(self, name, level, fn, lno, msg, args, exc_info, func=None, extra=None, sinfo=None):
"""Override default logger to allow overridding internal attributes."""
if six.PY2:
rv = logging.LogRecord(name, level, fn, lno, msg, args, exc_info, func)
else:
rv = logging.LogRecord(name, level, fn, lno, msg, args, exc_info, func, sinfo)
if extra is not None:
for key in extra:
# if (key in ["message", "asctime"]) or (key in rv.__dict__):
# raise KeyError("Attempt to overwrite %r in LogRecord" % key)
rv.__dict__[key] = extra[key]
return rv
logging.setLoggerClass(MyLogger)
logger = logging.getLogger(__name__)
Custom Exception Handler
class BaseCustomException(Exception):
"""Specified path was not found."""
def __init__(self, path):
"""Override message with defined const."""
try:
raise ZeroDivisionError
except ZeroDivisionError:
# Find the traceback frame that raised this exception
exception_frame = sys.exc_info()[2].tb_frame.f_back.f_back
exception_stack = traceback.extract_stack(exception_frame, limit=1)[0]
filename, lineno, funcName, tb_msg = exception_stack
extra = {'filename': os.path.basename(filename), 'lineno': lineno, 'funcName': funcName}
logger.debug(msg, extra=extra)
traceback.print_stack(exception_frame)
super(BaseCustomException, self).__init__(msg)