Python logging across multiple modules

Question

I'm trying to add logging (to console rather than a file) to my a piece of code I've been working on for a while. Having read around a bit I have a pattern that I think should work, but I'm not quite sure where I'm going wrong.

I have the following three files (simplified, obviously):

controller.py

import my_module    
import logging
from setup_log import configure_log

def main():
    logger = configure_log(logging.DEBUG, __name__)
    logger.info('Started logging')
    my_module.main()

if __name__ == "__main__":
    main()

setup_log.py

import logging

def configure_log(level=None, name=None):
    logger = logging.getLogger(name)
    logger.setLevel(level)
    console_handler = logging.StreamHandler()
    console_handler.setLevel(logging.DEBUG)
    chFormatter = logging.Formatter('%(levelname)s - %(filename)s - Line: %(lineno)d - %(message)s')
    console_handler.setFormatter(chFormatter)
    logger.addHandler(console_handler)
    return logger

my_module.py

import logging

def main():    
    logger = logging.getLogger(__name__)
    logger.info("Starting my_module")
    print "Something"

if __name__ == "__main__":
    main()

When I run them, only the first call to logging produces an output to console - 'Started logging'. The second call to logging - 'Starting my module' is just passed over.

What have I misunderstood/mangled?

Answer 1

According to the documentation it looks like you might get away with an even simpler setup like so:

If your program consists of multiple modules, here’s an example of how you could organize logging in it:

# myapp.py
import logging
import mylib

def main():
    logging.basicConfig(filename='myapp.log', level=logging.INFO)
    logging.info('Started')
    mylib.do_something()
    logging.info('Finished')

if __name__ == '__main__':
    main()

# mylib.py
import logging

def do_something():
    logging.info('Doing something')

If you run myapp.py, you should see this in myapp.log:

INFO:root:Started
INFO:root:Doing something
INFO:root:Finished

It looks like your call to logger = logging.getLogger(__name__) inside your module is creating a separate track (with a level of NOTSET but no parent relationship to result in a log entry)