Explanation of the relationship between python logging root logger and other loggers

01-explanation-of-python-logging-and-the-root-logger.md

Explanation of the relationship between python logging root logger and other loggers

02-main.py

import logging
import submodule
# Note that by importing submodule here before we've setup the root logger, all uses of logger in submodule outside of
# functions will not use the loglevel we set here in main.py

logging.basicConfig()

logger = logging.getLogger()
# Note that nothing is passed to getLogger
# By passing nothing, logger is set to the "root" logger
# If we instead set logger to logging.getLogger(__name__) other modules will not inherit the settings from this module

logger.setLevel(logging.INFO)

logger.error('This will display')
logger.info('This will display')
logger.debug('This will not display')


submodule.func()

03-submodule.py

import logging

logging.basicConfig()
logger = logging.getLogger(__name__)
# Here in the submodule, set logger to a logger called __name__
# This will help identify that log messages generated here came from this submodule
# We don't set the loglevel with setLevel because that loglevel is inherited from the parent module that calls imports this 
# submodule

logger.error('This will display')
logger.info('This will NOT display !!!')  # This will not display because we import submodule in main.py before we've setup the 
# root logger
logger.debug('This will not display')

def func():
  logger.error('func : This will display')
  logger.info('func : This will display')  # This will display because though we import submodule in main.py before we setup 
  # the root logger, we don't call the submodule.func function until after the root logger is setup
  logger.debug('func : This will not display')