Multiple Python Logging formats

I have been writing a python module that utilizes threading, and I wanted it to have a specific logging format so messages from separate threads could be differentiated. However, when the module was imported, it inherited any (root logger) format that was specified before it.

To achieve this goal, I tried the following things:

Setting the basicConfig

# basicConfig.py

import logging
logger = logging.getLogger(__name__)
FORMAT = "[%(levelname)s - %(filename)s - %(funcName)s] %(message)s"

logging.basicConfig(level=logging.DEBUG, format=FORMAT)


def info(msg):
	logger.info(msg)
def debug(msg):
	logger.debug(msg)
def warn(msg):
	logger.warn(msg)

Setting the basicConfig and disabling propagation

# basicConfig_noPropagate.py

import logging
logger = logging.getLogger(__name__)
FORMAT = "[%(levelname)s - %(module)s - %(funcName)s] %(message)s"

logging.basicConfig(level=logging.DEBUG, format=FORMAT)
logger.propagate = False

def info(msg):
	logger.info(msg)
def debug(msg):
	logger.debug(msg)
def warn(msg):
	logger.warn(msg)

Creating a new Handler

# handler.py

import logging
logger = logging.getLogger(__name__)
FORMAT = "[%(levelname)s - %(module)s - %(funcName)s] %(message)s"

logger.setLevel(logging.DEBUG)
ch = logging.StreamHandler()
ch.setFormatter(logging.Formatter(FORMAT))
logger.addHandler(ch)

def info(msg):
	logger.info(msg)
def debug(msg):
	logger.debug(msg)
def warn(msg):
	logger.warn(msg)

Creating a new Handler and disabling propagation

# handler_noPropagate.py

import logging
logger = logging.getLogger(__name__)
FORMAT = "[%(levelname)s - %(module)s - %(funcName)s] %(message)s"

logger.setLevel(logging.DEBUG)
ch = logging.StreamHandler()
ch.setFormatter(logging.Formatter(FORMAT))
logger.addHandler(ch)
logger.propagate = False

def info(msg):
	logger.info(msg)
def debug(msg):
	logger.debug(msg)
def warn(msg):
	logger.warn(msg)

Testing the the various methods

I then ran the following code to import and test various methods:

import logging
logger = logging.getLogger(__name__)
FORMAT = "[%(levelname)s - root - %(funcName)s] %(message)s"
logging.basicConfig(level=logging.INFO, format=FORMAT)
import basicConfig, handler, basicConfig_noPropagate, handler_noPropagate

def main():
	info("info")
	debug("debug")
	warn("warn")
	basicConfig.info("info from basicConfig")
	basicConfig.debug("debug from basicConfig")
	basicConfig.warn("warn from basicConfig")
	basicConfig_noPropagate.info("info from basicConfig_noPropagate")
	basicConfig_noPropagate.debug("debug from basicConfig_noPropagate")
	basicConfig_noPropagate.warn("warn from basicConfig_noPropagate")
	handler.info("info from handler")
	handler.debug("debug from handler")
	handler.warn("warn from handler")
	handler_noPropagate.info("info from handler_noPropagate")
	handler_noPropagate.debug("debug from handler_noPropagate")
	handler_noPropagate.warn("warn from handler_noPropagate")

def info(msg):
	logger.info(msg)
def debug(msg):
	logger.debug(msg)
def warn(msg):
	logger.warn(msg)

if __name__ == "__main__":
	main()

which output

[INFO - root - info] info
[WARNING - root - warn] warn
[INFO - root - info] info from basicConfig
[WARNING - root - warn] warn from basicConfig
No handlers could be found for logger "basicConfig_noPropagate"
[INFO - handler - info] info from handler
[INFO - root - info] info from handler
[DEBUG - handler - debug] debug from handler
[DEBUG - root - debug] debug from handler
[WARNING - handler - warn] warn from handler
[WARNING - root - warn] warn from handler
[INFO - handler_noPropagate - info] info from handler_noPropagate
[DEBUG - handler_noPropagate - debug] debug from handler_noPropagate
[WARNING - handler_noPropagate - warn] warn from handler_noPropagate

and tells me the following:

Method	Printed log messages	Updated Formatter	Updated logging level	No duplicated messages
`basicConfig.py`	X			X
`basicConfig_noPropagate.py`
`handler.py`	X	X	X
`handler_noPropagate.py`	X	X	X	X

This means if you want your library to have a custom Formatter and level that is not overwritten, you must

import logging
# Create local logger
logger = logging.getLogger(__name__)
# Define new format string
FORMAT = "[%(levelname)s - %(module)s - %(funcName)s] %(message)s"
# Set desired logging level
logger.setLevel(logging.DEBUG)
# Create new console stream (could be file too)
ch = logging.StreamHandler()
# Update the formatter of the new stream
ch.setFormatter(logging.Formatter(FORMAT))
# Add the handler to the logger
logger.addHandler(ch)
# Disable message propagation to prevent duplicate messages
logger.propagate = False

26 Sep 2019