How to write to a file, using the logging Python module?

Question

How can I use the logging module in Python to write to a file? Every time I try to use it, it just prints out the message.

Answer 1

Taken from the "logging cookbook":

# create logger with 'spam_application'
logger = logging.getLogger('spam_application')
logger.setLevel(logging.DEBUG)
# create file handler which logs even debug messages
fh = logging.FileHandler('spam.log')
fh.setLevel(logging.DEBUG)
logger.addHandler(fh)

And you're good to go.

P.S. Make sure to read the logging HOWTO as well.

Answer 2

An example of using logging.basicConfig rather than logging.fileHandler()

logging.basicConfig(filename=logname,
                            filemode='a',
                            format='%(asctime)s,%(msecs)d %(name)s %(levelname)s %(message)s',
                            datefmt='%H:%M:%S',
                            level=logging.DEBUG)

logging.info("Running Urban Planning")

self.logger = logging.getLogger('urbanGUI')

In order, the five parts do the following:

1. set the output file (filename=logname)
2. set it to append rather than overwrite (filemode='a')
3. determine the format of the output message (format=...)
4. determine the format of the output time (datefmt='%H:%M:%S')
5. and determine the minimum message level it will accept (level=logging.DEBUG).

Answer 3

import sys
import logging

from util import reducer_logfile
logging.basicConfig(filename=reducer_logfile, format='%(message)s',
                    level=logging.INFO, filemode='w')

Answer 4

I prefer to use a configuration file. It allows me to switch logging levels, locations, etc without changing code when I go from development to release. I simply package a different config file with the same name, and with the same defined loggers.

import logging.config
if __name__ == '__main__':
    # Configure the logger
    # loggerConfigFileName: The name and path of your configuration file
    logging.config.fileConfig(path.normpath(loggerConfigFileName))

    # Create the logger
    # Admin_Client: The name of a logger defined in the config file
    mylogger = logging.getLogger('Admin_Client')

    msg='Bite Me'
    myLogger.debug(msg)
    myLogger.info(msg)
    myLogger.warn(msg)
    myLogger.error(msg)
    myLogger.critical(msg)

    # Shut down the logger
    logging.shutdown()

Here is my code for the log config file

#These are the loggers that are available from the code
#Each logger requires a handler, but can have more than one
[loggers]
keys=root,Admin_Client


#Each handler requires a single formatter
[handlers]
keys=fileHandler, consoleHandler


[formatters]
keys=logFormatter, consoleFormatter


[logger_root]
level=DEBUG
handlers=fileHandler


[logger_Admin_Client]
level=DEBUG
handlers=fileHandler, consoleHandler
qualname=Admin_Client
#propagate=0 Does not pass messages to ancestor loggers(root)
propagate=0


# Do not use a console logger when running scripts from a bat file without a console
# because it hangs!
[handler_consoleHandler]
class=StreamHandler
level=DEBUG
formatter=consoleFormatter
args=(sys.stdout,)# The comma is correct, because the parser is looking for args


[handler_fileHandler]
class=FileHandler
level=DEBUG
formatter=logFormatter
# This causes a new file to be created for each script
# Change time.strftime("%Y%m%d%H%M%S") to time.strftime("%Y%m%d")
# And only one log per day will be created. All messages will be amended to it.
args=("D:\\Logs\\PyLogs\\" + time.strftime("%Y%m%d%H%M%S")+'.log', 'a')


[formatter_logFormatter]
#name is the name of the logger root or Admin_Client
#levelname is the log message level debug, warn, ect 
#lineno is the line number from where the call to log is made
#04d is simple formatting to ensure there are four numeric places with leading zeros
#4s would work as well, but would simply pad the string with leading spaces, right justify
#-4s would work as well, but would simply pad the string with trailing spaces, left justify
#filename is the file name from where the call to log is made
#funcName is the method name from where the call to log is made
#format=%(asctime)s | %(lineno)d | %(message)s
#format=%(asctime)s | %(name)s | %(levelname)s | %(message)s
#format=%(asctime)s | %(name)s | %(module)s-%(lineno) | %(levelname)s | %(message)s
#format=%(asctime)s | %(name)s | %(module)s-%(lineno)04d | %(levelname)s | %(message)s
#format=%(asctime)s | %(name)s | %(module)s-%(lineno)4s | %(levelname)-8s | %(message)s

format=%(asctime)s | %(levelname)-8s | %(lineno)04d | %(message)s


#Use a separate formatter for the console if you want
[formatter_consoleFormatter]
format=%(asctime)s | %(levelname)-8s | %(filename)s-%(funcName)s-%(lineno)04d | %(message)s

Answer 5

This example should work fine. I have added streamhandler for console. Console log and file handler data should be similar.

    # MUTHUKUMAR_TIME_DATE.py #>>>>>>>> file name(module)

    import sys
    import logging
    import logging.config
    # ================== Logger ================================
    def Logger(file_name):
        formatter = logging.Formatter(fmt='%(asctime)s %(module)s,line: %(lineno)d %(levelname)8s | %(message)s',
                                      datefmt='%Y/%m/%d %H:%M:%S') # %I:%M:%S %p AM|PM format
        logging.basicConfig(filename = '%s.log' %(file_name),format= '%(asctime)s %(module)s,line: %(lineno)d %(levelname)8s | %(message)s',
                                      datefmt='%Y/%m/%d %H:%M:%S', filemode = 'w', level = logging.INFO)
        log_obj = logging.getLogger()
        log_obj.setLevel(logging.DEBUG)
        # log_obj = logging.getLogger().addHandler(logging.StreamHandler())

        # console printer
        screen_handler = logging.StreamHandler(stream=sys.stdout) #stream=sys.stdout is similar to normal print
        screen_handler.setFormatter(formatter)
        logging.getLogger().addHandler(screen_handler)

        log_obj.info("Logger object created successfully..")
        return log_obj
    # =======================================================


MUTHUKUMAR_LOGGING_CHECK.py #>>>>>>>>>>> file name
# calling **Logger** function
file_name = 'muthu'
log_obj =Logger(file_name)
log_obj.info("yes   hfghghg ghgfh".format())
log_obj.critical("CRIC".format())
log_obj.error("ERR".format())
log_obj.warning("WARN".format())
log_obj.debug("debug".format())
log_obj.info("qwerty".format())
log_obj.info("asdfghjkl".format())
log_obj.info("zxcvbnm".format())
# closing file
log_obj.handlers.clear()

OUTPUT:
2019/07/13 23:54:40 MUTHUKUMAR_TIME_DATE,line: 17     INFO | Logger object created successfully..
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 8     INFO | yes   hfghghg ghgfh
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 9 CRITICAL | CRIC
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 10    ERROR | ERR
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 11  WARNING | WARN
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 12    DEBUG | debug
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 13     INFO | qwerty
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 14     INFO | asdfghjkl
2019/07/13 23:54:40 MUTHUKUMAR_LOGGING_CHECK,line: 15     INFO | zxcvbnm

Thanks, 

Answer 6

here's a simpler way to go about it. this solution doesn't use a config dictionary and uses a rotation file handler, like so:

import logging
from logging.handlers import RotatingFileHandler

logging.basicConfig(handlers=[RotatingFileHandler(filename=logpath+filename,
                     mode='w', maxBytes=512000, backupCount=4)], level=debug_level,
                     format='%(levelname)s %(asctime)s %(message)s', 
                    datefmt='%m/%d/%Y%I:%M:%S %p')

logger = logging.getLogger('my_logger')

or like so:

import logging
from logging.handlers import RotatingFileHandler

handlers = [
            RotatingFileHandler(filename=logpath+filename, mode='w', maxBytes=512000, 
                                backupCount=4)
           ]
logging.basicConfig(handlers=handlers, level=debug_level, 
                    format='%(levelname)s %(asctime)s %(message)s', 
                    datefmt='%m/%d/%Y%I:%M:%S %p')

logger = logging.getLogger('my_logger')

the handlers variable needs to be an iterable. logpath+filename and debug_level are just variables holding the respective info. of course, the values for the function params are up to you.

the first time i was using the logging module i made the mistake of writing the following, which generates an OS file lock error (the above is the solution to that):

import logging
from logging.handlers import RotatingFileHandler

logging.basicConfig(filename=logpath+filename, level=debug_level, format='%(levelname)s %(asctime)s %(message)s', datefmt='%m/%d/%Y
 %I:%M:%S %p')

logger = logging.getLogger('my_logger')
logger.addHandler(RotatingFileHandler(filename=logpath+filename, mode='w', 
                  maxBytes=512000, backupCount=4))

and Bob's your uncle!