Logging to file and not to console in Python

Question

I have an application which sets up logging after parsing the args in the main() funktion. It needs to be setup after parsing the args because I can set the loglevel via commandline flags.

I have tried many variants on how to do that but every time with an weird result. What I want is logging in from all libs and really understand that doing this should be enough there:

from logging import getLogger

logger = getLogger(__name__)

But, I need to setup the logger in the main() function to log only to a file and not to console because my application has an own shell interface which should not be spammed with log messages - never a message should show up there.

I think it should be only some few lines of code but I can't figure that out. The logger should be configured to have a max file size and rotate logfiles. Can someone help me with this?

Answer 1

import logging
import logging.handlers

logger = logging.getLogger(__name__)

def levelnames():
 try:
 names = logging._nameToLevel
 except AttributeError:
 names = (name for name in logging._levelNames if isinstance(name, 
str))

def main():
 import argparse
 parser = argparse.ArgumentParser()
 parser.add_argument("--logging-file", default="tmp.log")
 parser.add_argument("--logging-level", choices=levelnames(), 
default="INFO")
 args = parser.parse_args()

 root = logging.getLogger()

 formatter = logging.Formatter(logging.BASIC_FORMAT)
 handler = logging.handlers.RotatingFileHandler(args.logging_file, 
maxBytes=100, backupCount=3)
 handler.setFormatter(formatter)

 root.addHandler(handler)
 root.setLevel(args.logging_level)

 logger.info("your info")
 logger.warn("your warning")
 logger.critical("your critical message")

if __name__ == "__main__":
 main()

Does this do what you want? (maxBytes is probably a bit low)

Comments

Yes! That was exactly what I want! Thank you very much! Now it behaves well. I know that maxBytes is slow but that will be configurable in the future. I just needed some clean way to get debug messages even from libs like APScheduler. When running my application in production mode logging will be completely disabled so it is Ok this way.