python logging module is not writing anything to file

Question

I'm trying to write a server that logs exceptions both to the console and to a file. I pulled some code off the cookbook. Here it is:

logger = logging.getLogger('server_logger')
logger.setLevel(logging.DEBUG)
# create file handler which logs even debug messages
fh = logging.FileHandler('server.log')
fh.setLevel(logging.DEBUG)
# create console handler with a higher log level
ch = logging.StreamHandler()
ch.setLevel(logging.ERROR)
# create formatter and add it to the handlers
formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s', datefmt='%Y-%m-%d %H:%M:%S')
ch.setFormatter(formatter)
fh.setFormatter(formatter)
# add the handlers to logger
logger.addHandler(ch)
logger.addHandler(fh)

This code logs perfectly fine to the console, but nothing is logged to the file. The file is created, but nothing is ever written to it. I've tried closing the handler, but that doesn't do anything. Neither does flushing it. I searched the Internet, but apparently I'm the only one with this problem. Does anybody have any idea what the problem is? Thanks for your answers.

Vi

What command are you using to log? Are you just calling logging.debug()? – Flywheel

I'm using logging.error() – Vi

No repro for me. Your code works as expected – Keeper

Answer 1

Try calling

logger.error('This should go to both console and file')

instead of

logging.error('this will go to the default logger which you have not changed the config of')

Flywheel

Oh hey! This totally made it work! You're a genius! Although I don't totally understand why that made it work... – Vi

Calling logging.error uses the default logger, which you have not configured. The variable logger is the one you defined in the first line, which has all the properties you configured. – Flywheel

still empty wth, i did this already – Monocle

Answer 2

Try to put the import and the basicConfig at the very beggining of the script. Something like this:

import logging
logging.basicConfig(filename='log.log', level=logging.INFO)
.
.
import ...
import ...

Chambray

Thanks for this! I know it's not the answer to this question (OP's problem was using logging.debug/info/error() instead of logger.debug/info/error() ), but this fixed a problem I was having. Using "import h2o" made my logging.basicConfig() call down below it ineffective. I'm guessing something in the h2o module initializes the logging module... genius move by whoever decided to do that. – Ilailaire

Fixed mine as well - I was trying to log something within a unittest. It worked fine then I must have broken something. Bringing the config up fixed it. – Boeke

This solved my problem as well ; I was importing gensim which has its own logger. Thanks! – Riot

Solved for me as well! – Binnie

This was the reason my logging was not working - thanks! – Siderite

Answer 3

Put this

for handler in logging.root.handlers[:]:
    logging.root.removeHandler(handler)

in front of the

logging.basicConfig(...)

see also Logging module not writing to file

Herd

This is perfect! Keeps from having to initialize log before other imports and handles extraneous handlers created in other imported modules (way to handle things!) – Spineless

Answer 4

I know that this question might be a bit too old but I found the above method a bit of an overkill. I ran into a similar issue, I was able to solve it by:

import logging

logging.basicConfig(format = '%(asctime)s %(message)s',
                    datefmt = '%m/%d/%Y %I:%M:%S %p',
                    filename = 'example.log',
                    level=logging.DEBUG)

This will write to example.log all logs that are of level debug or higher.

logging.debug("This is a debug message") will write This is a debug message to example.log. Level is important for this to work.

Marinamarinade

I also thought the OP was a bit overkill for what I wanted to do. I'm trying to make the code you have working, but it doesn't create any file for me, let alone write in it. – Backchat

@Backchat - docs.python.org/2/howto/logging.html#logging-to-a-file. I hope this helps you out. – Marinamarinade

@AbassSesay - Thank you, I didn't specify the level and it was failing. – Floydflss

the file doesnt even created with this approach, im confused – Monocle

Answer 5

In order to both write to terminal and file you can do like below:

import logging.config

logging.basicConfig(
    level=logging.INFO,
    format="%(asctime)s [%(levelname)s] %(message)s",
    handlers=[
        logging.FileHandler("log_file.log"),
        logging.StreamHandler()
    ]
)
logger = logging.getLogger(__name__)

usage in the code:

logger.info('message')
logger.error('message')

Fania

Answer 6

If root.handlers is not empty, log file will not be created. We should empty root.handlers before calling basicConfig() method. source

Snippet:

for handler in logging.root.handlers[:]:
logging.root.removeHandler(handler)

The full code is below:

import logging
##loging
for handler in logging.root.handlers[:]:
    logging.root.removeHandler(handler)

logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s %(message)s',
                    datefmt='%a, %d %b %Y %H:%M:%S',
                    filename= 'log.txt',
                    filemode='w')

console = logging.StreamHandler()
console.setLevel(logging.INFO)
# add the handler to the root logger
logging.getLogger().addHandler(console)
logging.info("\nParameters:")

for i in range(10):
    logging.info(i)

logging.info("end!")

Garrity