Should A Python Logger Be Passed As Parameter?

A Python application we're developing requires a logger. A coworker argues that the logger should be created and configured in every class that's using it. My opinion is that it sh

Solution 1:

Not usually; it is typically not meant to be passed as a parameter.

The convention is to use log = logging.getLogger(__name__) in the top of each module. The value of __name__ is different for each module. The resultant value of __name__ can then be reflected in each log message.

Solution 2:

Maybe this helps you to get an idea? Of course you can make it much better, reading settings from a config file or whatever but this is quick example.

A separate module to configure the logging: mylogmod.py :

import logging

FILENAME = "mylog.log" # Your logfile
LOGFORMAT = "%(message)s" # Your format
DEFAULT_LEVEL = "info" # Your default level, usually set to warning or error for production
LEVELS = {
    'debug':logging.DEBUG,
    'info':logging.INFO,
    'warning':logging.WARNING,
    'error':logging.ERROR,
    'critical':logging.CRITICAL}

def startlogging(filename=FILENAME, level=DEFAULT_LEVEL):
    logging.basicConfig(filename=filename, level=LEVELS[level], format=LOGFORMAT)

The main.py :

import logging
from mylogmod import startlogging
from myclass import MyClass

startlogging()

logging.info("Program started...")
mc = MyClass()

A class myclass.py from a module with self test. You can do something similar in a unittest: (Note that you don't need to import the logging module in a unittest, just the startlogging function is enough. This way you can set the default level to warning or error and the unittests and self tests to debug)

import logging

class MyClass(object):
    def __init__(self):
        logging.info("Initialze MyClass instance...")

if __name__ == "__main__":
    from mylogmod import startlogging
    startlogging(level="debug")
    logging.debug("Test MyClass...")
    #... rest of test code...

Solution 3:

I think passing logger as parameter isn't good idea. You should consider a global logger as own module, it would be the best idea. For example:
logger.py

import logging
log = logging.getLogger('')

classFoo.py

form logger import log
log.debug('debug message')

classBar.py

form logger import log
log.warn('warn!')