Develop Reference

Log files get reset on the restart of the application instead of appending the new logs to it

import logging
def setup_logger(logger_name, log_file, level=logging.DEBUG):
l = logging.getLogger(logger_name)
formatter = logging.Formatter('%(asctime)s : %(levelname)s : %(message)s')
fileHandler = logging.FileHandler(log_file, mode='w')
fileHandler.setFormatter(formatter)
streamHandler = logging.StreamHandler()
streamHandler.setFormatter(formatter)
l.setLevel(level)
l.addHandler(fileHandler)
l.addHandler(streamHandler)
I'm trying to write the different logs(levels) to the different files the functionality is working fine but when ever the application is restarted the log files get reset instead of appending the data to it.
#method called from the different method
setup_logger('logger', 'login.log')
setup_logger('logger_market', 'transaction.log')
logger = logging.getLogger('logger')
logger_market = logging.getLogger('logger_market')
logger.info(f'Test for the login.log file')
logger_market.info(f'this to test')
I'm new to logging in python and the documentation is a bit complex for me at the moment.

I think you do not need to set mode
just use following: fileHandler = logging.FileHandler(log_file)

Python multiple loggers not working. How to configure multiple loggers with different levels?

I am trying to configure two loggers, one logger is for INFO level, and the other logger is for DEBUG level. I would like DEBUG content to only go to my log file, and I would like the INFO content to go both a log file and to the console. Please see the below code. Nothing is being written into my files and nothing is being displayed in the console.
logFileDir = os.path.join(os.getcwd(), '.logs')
if not os.path.exists(logFileDir):
os.mkdir(logFileDir)
infoLogFileDir = os.path.join(logFileDir, 'INFO')
if not os.path.exists(infoLogFileDir):
os.mkdir(infoLogFileDir)
debugLogFileDir = os.path.join(logFileDir, 'DEBUG')
if not os.path.exists(debugLogFileDir):
os.mkdir(debugLogFileDir)
LOG_FORMAT = ("%(asctime)s [%(levelname)s]: %(message)s in %(pathname)s:%(lineno)d")
#DEBUG LOGGER
debugLogFileName = os.path.join(debugLogFileDir, 'EFDebugLog.log')
debugLogger = logging.getLogger("debugLogger")
debugLogger.setLevel(logging.DEBUG)
debugHandler = logging.handlers.RotatingFileHandler(filename=debugLogFileName,maxBytes=5000000, backupCount=100)
debugHandler.setLevel(logging.DEBUG)
debugHandler.setFormatter(Formatter(LOG_FORMAT))
debugLogger.addHandler(debugHandler)
#INFO LOGGER
infoLogFileName = os.path.join(infoLogFileDir, 'EFInfoLog.log')
infoLogger = logging.getLogger("infoLogger")
infoLogger.setLevel(logging.INFO)
infoHandler = logging.handlers.RotatingFileHandler(filename=infoLogFileName,maxBytes=5000000, backupCount=100)
infoHandler.setLevel(logging.INFO)
infoHandler.setFormatter(Formatter(LOG_FORMAT))
infoLogger.addHandler(infoHandler)
infoLogger.addHandler(logging.StreamHandler())

The logging.* functions that you are calling log to the root logger. That's why you don't see any output; you haven't configured any handlers for the root logger. You have only configured handlers for your own loggers, which you are not using.
If you want to use the logging.* functions, you need to first configure the root logger, which you can get by calling getLogger without any arguments. So the code might look like:
import logging
import logging.handlers
root_logger = logging.getLogger()
info_handler = logging.handlers.RotatingFileHandler(filename='infolog.txt')
info_handler.setLevel(logging.INFO)
stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging.INFO)
debug_handler = logging.handlers.RotatingFileHandler(filename='debuglog.txt')
debug_handler.setLevel(logging.DEBUG)
root_logger.addHandler(stream_handler)
root_logger.addHandler(debug_handler)
root_logger.addHandler(info_handler)
# this is needed, since the severity is WARNING by default,
# i.e. it would not log any debug messages
root_logger.setLevel(logging.DEBUG)
root_logger.debug('this is a debug message')
root_logger.info('this is an info message')

Python logging - new log file each loop iteration

I would like to generate a new log file on each iteration of a loop in Python using the logging module. I am analysing data in a for loop, where each iteration of the loop contains information on a new object. I would like to generate a log file per object.
I looked at the docs for the logging module and there is capability to change log file on time intervals or when the log file fills up, but I cannot see how to iteratively generate a new log file with a new name. I know ahead of time how many objects are in the loop.
My imagined pseudo code would be:
import logging
for target in targets:
logfile_name = f"{target}.log"
logging.basicConfig(format='%(asctime)s - %(levelname)s : %(message)s',
datefmt='%Y-%m/%dT%H:%M:%S',
filename=logfile_name,
level=logging.DEBUG)
# analyse target infomation
logging.info('log target info...')
However, the logging information is always appended to the fist log file for target 1.
Is there a way to force a new log file at the beginning of each loop?

Rather than using logging directly, you need to use logger objects. Go thorough the docs here.
Create a new logger object as a first statement in the loop. The below is a working solution.
import logging
import sys
def my_custom_logger(logger_name, level=logging.DEBUG):
"""
Method to return a custom logger with the given name and level
"""
logger = logging.getLogger(logger_name)
logger.setLevel(level)
format_string = ("%(asctime)s — %(name)s — %(levelname)s — %(funcName)s:"
"%(lineno)d — %(message)s")
log_format = logging.Formatter(format_string)
# Creating and adding the console handler
console_handler = logging.StreamHandler(sys.stdout)
console_handler.setFormatter(log_format)
logger.addHandler(console_handler)
# Creating and adding the file handler
file_handler = logging.FileHandler(logger_name, mode='a')
file_handler.setFormatter(log_format)
logger.addHandler(file_handler)
return logger
if __name__ == "__main__":
for item in range(10):
logger = my_custom_logger(f"Logger{item}")
logger.debug(item)
This writes to a different log file for each iteration.

This might not be the best solution, but it will create new log file for each iteration. What this is doing is, adding a new file handler in each iteration.
import logging
targets = ["a", "b", "c"]
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
for target in targets:
log_file = "{}.log".format(target)
log_format = "|%(levelname)s| : [%(filename)s]--[%(funcName)s] : %(message)s"
formatter = logging.Formatter(log_format)
# create file handler and set the formatter
file_handler = logging.FileHandler(log_file)
file_handler.setFormatter(formatter)
# add handler to the logger
logger.addHandler(file_handler)
# sample message
logger.info("Log file: {}".format(target))

This is not necessarily the best answer but worked for my case, and just wanted to put it here for future references. I created a function that looks as follows:
def logger(filename, level=None, format=None):
"""A wrapper to the logging python module
This module is useful for cases where we need to log in a for loop
different files. It also will allow more flexibility later on how the
logging format could evolve.
Parameters
----------
filename : str
Name of logfile.
level : str, optional
Level of logging messages, by default 'info'. Supported are: 'info'
and 'debug'.
format : str, optional
Format of logging messages, by default '%(message)s'.
Returns
-------
logger
A logger object.
"""
levels = {"info": logging.INFO, "debug": logging.DEBUG}
if level is None:
level = levels["info"]
else:
level = levels[level.lower()]
if format is None:
format = "%(message)s"
# https://stackoverflow.com/a/12158233/1995261
for handler in logging.root.handlers[:]:
logging.root.removeHandler(handler)
logger = logging.basicConfig(filename=filename, level=level, format=format)
return logger
As you can see (you might need to scroll down the code above to see the return logger line), I am using logging.basicConfig(). All modules I have in my package that log stuff, have the following at the beginning of the files:
import logging
import other stuff
logger = logging.getLogger()
class SomeClass(object):
def some_method(self):
logger.info("Whatever")
.... stuff
When doing a loop, I have call things this way:
if __name__ == "__main__":
for i in range(1, 11, 1):
directory = "_{}".format(i)
if not os.path.exists(directory):
os.makedirs(directory)
filename = directory + "/training.log"
logger(filename=filename)
I hope this is helpful.

I'd like to slightly modify #0Nicholas's method. The direction is right, but the first FileHandler will continue log information into the first log file as long as the function is running. Therefore, we would want to pop the handler out of the logger's handlers list:
import logging
targets = ["a", "b", "c"]
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
log_format = "|%(levelname)s| : [%(filename)s]--[%(funcName)s] : %(message)s"
formatter = logging.Formatter(log_format)
for target in targets:
log_file = f"{target}.log"
# create file handler and set the formatter
file_handler = logging.FileHandler(log_file)
file_handler.setFormatter(formatter)
# add handler to the logger
logger.addHandler(file_handler)
# sample message
logger.info(f"Log file: {target}")
# close the log file
file_handler.close()
# remove the handler from the logger. The default behavior is to pop out
# the last added one, which is the file_handler we just added in the
# beginning of this iteration.
logger.handlers.pop()

Here is a working version for this problem. I was only able to get it to work if the targets already have .log before going into the loop so you may want to add one more for before going into targets and override all targets with .log extension
import logging
targets = ["a.log","b.log","c.log"]
for target in targets:
log = logging.getLogger(target)
formatter = logging.Formatter('%(asctime)s - %(levelname)s : %(message)s', datefmt='%Y-%m/%dT%H:%M:%S')
fileHandler = logging.FileHandler(target, mode='a')
fileHandler.setFormatter(formatter)
streamHandler = logging.StreamHandler()
streamHandler.setFormatter(formatter)
log.addHandler(fileHandler)
log.addHandler(streamHandler)
log.info('log target info...')

Confused when using Python logging module

I want to log to 2 different files, but different things.
I was trying this:
runid = str(uuid.uuid1())
logger = logging.getLogger('logger1')
other_logger = logging.getLogger('logger2')
logger.setLevel(logging.DEBUG)
debug_handler = logging.FileHandler('log/debug.log')
info_handler = logging.FileHandler('log/info.log')
other_handler = logging.FileHandler('log/other_info.log')
debug_handler.setLevel(logging.DEBUG)
info_handler.setLevel(logging.INFO)
other_handler.setLevel(logging.INFO)
formatter = logging.Formatter(runid + ' - %(asctime)s - %(levelname)s - %(funcName)s - %(message)s')
debug_handler.setFormatter(formatter)
info_handler.setFormatter(formatter)
other_handler.setFormatter(formatter)
logger.addHandler(debug_handler)
logger.addHandler(info_handler)
other_logger.addHandler(other_handler)
logger.info('message1')
other_logger.info('message2')
But logger and other_logger are working as one and I get both messages in all files, no matter if I call in logger or other_logger.
According doc:
"Loggers have the following attributes and methods. Note that Loggers
are never instantiated directly, but always through the module-level
function logging.getLogger(name). Multiple calls to getLogger() with
the same name will always return a reference to the same Logger
object."
But the parent object is always the same, as in this small test:
import logging
log1 = logging.getLogger('hey')
log2 = logging.getLogger('you')
print log1.parent, log2.parent
enrique#enrique-mbp:$ python /tmp/test.py
<logging.RootLogger object at 0x26f0810> <logging.RootLogger object at 0x26f0810>
How can I solve this?

The problem is here:
logger.setLevel(logging.DEBUG)
You need to set the level for other_logger as well:
logger.setLevel(logging.DEBUG)
other_logger.setLevel(logging.DEBUG) # or INFO because that is the lowest level being used by a handler
Without this, other_logger remains at the default logging level, logging.WARNING, which prevents the other_logger.info('message2') line from logging anything.

Python logger not respecting setLevel?

I've spent a bit of time looking through the site at Python logger questions hoping my would be resolved there. I've set up a logger with two stream handlers that have both different formats and levels of logging, here's a functional snippet from my codebase:
import os
import time
import logging
LOG_LEVELS = [logging.ERROR, logging.WARNING, logging.INFO, logging.DEBUG]
TEST_RESULT_LEVELV_NUM = 51
# http://stackoverflow.com/a/11784984/196832
def status(self, message, *args, **kws):
self._log(TEST_RESULT_LEVELV_NUM, message, args, **kws)
logging.addLevelName(TEST_RESULT_LEVELV_NUM, "RESULT")
logging.Logger.result = status
def setup_logging(level=0, quiet=False, logdir=None):
logger = logging.getLogger('juju-test')
ffmt = logging.Formatter('%(asctime)s %(name)s %(levelname)-8s: %(message)s')
cfmt = logging.Formatter('%(name)s %(levelname)s: %(message)s')
#logger.setLevel(0)
if level >= len(LOG_LEVELS):
level = len(LOG_LEVELS) - 1
if logdir:
if not os.path.exists(logdir):
os.makedirs(logdir)
logfile = os.path.join(logdir, 'juju-test.%s.log' % int(time.time()))
fh = logging.FileHandler(logfile)
# Always at least log to INFO for file, unless DEBUG is requested
fh.setLevel(LOG_LEVELS[level if level >= 2 else 2])
fh.setFormatter(ffmt)
logger.addHandler(fh)
if not quiet:
ch = logging.StreamHandler()
ch.setLevel(LOG_LEVELS[level])
ch.setFormatter(cfmt)
logger.addHandler(ch)
return logger
I've been using an argparse to feed this, but for testing purposes if you feed the following to function:
logger = setup_logging(level=1, logdir="/tmp/oofrab/")
logger.info('Informative!')
logger.warn('Whoa buddy!')
logger.error('Look what you did.')
logger.result("They told me not to make a custom logging level, I'll show them!")
logger.debug('Lots of bugs, man')
I'd expect to see status, error, and warn in the console. Then status, error, warn and info in the log. However, I only see down to warn in both console and log file, despite selecting logging.INFO (key 2 in the LOG_LEVELS list) for the file handler. Is this expected?
I'm not using basicConfig or anything else when building the logger, why can't I have these two custom levels?

Apparently, logging.NOTSET does not mean "All levels", but rather defaults. So setting the parent logger to level 0 does only reverts it to it's default accepted levels. That being said, if I set logger.setLevel to logging.DEBUG that essentially sets logging to accept ALL levels then passes filtering on to the various handlers to filter further.
To get around this (and potential custom log levels) I've set the initial logger level to 1