How to log exceptions in Python

Sometimes it is useful to just catch any exception, write details to a log file and continue execution.

In the Python standard library, it is possible to use the logging and exceptions modules to achieve this. First of all, we want to catch any exception, but also being able to access all information about it:

try:
    my_function_1()
except exception.Exception as e:
    print e.__class__, e.__doc__, e.message

Then we want to write those to a logging file, so we need to setup the logging module:

import logging
logging.basicConfig( filename="main.log",
                     filemode='w',
                     level=logging.DEBUG,
                     format= '%(asctime)s - %(levelname)s - %(message)s',
                   )

In the following gist everything together, with also function name detection from Alex Martelli:

	import sys
	import traceback
	import logging
	def setup_logging_to_file(filename):
	logging.basicConfig( filename=filename,
	filemode='w',
	level=logging.DEBUG,
	format= '%(asctime)s - %(levelname)s - %(message)s',
	)
	def extract_function_name():
	"""Extracts failing function name from Traceback
	by Alex Martelli
	http://stackoverflow.com/questions/2380073/\
	how-to-identify-what-function-call-raise-an-exception-in-python
	"""
	tb = sys.exc_info()[-1]
	stk = traceback.extract_tb(tb, 1)
	fname = stk[0][3]
	return fname
	def log_exception(e):
	logging.error(
	"Function {function_name} raised {exception_class} ({exception_docstring}): {exception_message}".format(
	function_name = extract_function_name(), #this is optional
	exception_class = e.__class__,
	exception_docstring = e.__doc__,
	exception_message = e.message))

view raw logging_utils.py hosted with ❤ by GitHub

	import exceptions
	import sys, os
	from logging_utils import setup_logging_to_file, log_exception
	from my_module import my_function_1, my_function_2
	if __name__ == "__main__":
	setup_logging_to_file("main.log")
	try:
	my_function_1()
	except exceptions.Exception as e:
	# we do not want to stop execution, just log and continue
	log_exception(e)
	try:
	my_function_2()
	except exceptions.Exception as e:
	log_exception(e)
	def my_function_1_wrapper():
	my_function_1()
	# in this case the log message is logging the wrapper as function name
	try:
	my_function_1_wrapper()
	except exceptions.Exception as e:
	log_exception(e)

view raw main.py hosted with ❤ by GitHub

	import exceptions
	class MyException(exceptions.Exception):
	"""This is my own Exception"""
	def my_function_1():
	raise exceptions.IndexError("Some indexing error")
	def my_function_2():
	e = MyException("Something went quite wrong")
	raise e

view raw my_module.py hosted with ❤ by GitHub

Here the output log:

2013-10-01 11:32:56,466 - ERROR - Function my_function_1() raised <type 'exceptions.IndexError'> (Sequence index out of range.): Some indexing error
2013-10-01 11:32:56,466 - ERROR - Function my_function_2() raised <class 'my_module.MyException'> (This is my own Exception): Something went quite wrong
2013-10-01 11:32:56,466 - ERROR - Function my_function_1_wrapper() raised <type 'exceptions.IndexError'> (Sequence index out of range.): Some indexing error