Python logging example

The native logging class in Python can be a little cumbersome and daunting to use. I've combined the use of ArgParse along with some simple use of logging as an example that solves a lot of problems I often want to solve:

	#! /usr/bin/env python
	import logging
	import argparse
	parser = argparse.ArgumentParser()
	group = parser.add_mutually_exclusive_group()
	group.add_argument('-v', '--verbose', dest='verbose', action='count', help='Enable debugging - multiple uses prints more messages')
	group.add_argument('--loglevel', dest='loglevel', action='store', help='Set log level: DEBUG, INFO, WARNING, ERROR, CRITICAL')
	args = parser.parse_args()
	logging.basicConfig(format='%(asctime)s %(levelname)s %(pathname)s:%(lineno)d %(msg)s')
	log = logging.getLogger()
	log.setLevel(args.loglevel or (logging.WARNING - (args.verbose or 0) * 10))
	log.debug('This is a debugging message')
	log.info('This is an informational message')
	log.warn('This is a warning message')
	log.error('This is an error message')
	log.fatal('This is a fatal/critical message')

view raw log_example hosted with ❤ by GitHub

I figure I'll refer to this example when I want to make use of logging in scripts in the future.

This example does the following:

• Default logging level is to print warning, error, and fatal/critical error messages. Debugging and warning messages are not printed
• Using one -v option prints all of the messages above including informational messages
• Using two -v options prints all of the messages above including debugging messages
• Using three or more -v options does not change the behavior from using two options. There is no error but there is no benefit to additional options either
• You can specify an explicit log level and even reduce messages using -loglevel LEVEL where LEVEL must be one of:
  • DEBUG
  • INFO
  • WARNING
  • ERROR
  • CRITICAL
  The script support the use of FATAL which is just synonymous with CRITICAL.
  The -loglevel LEVEL and -v options are mutually exclusive.
• There's no way to dispose of messages altogether through the options but it can be done by redirecting stderr to /dev/null
• A custom format includes elements of the error that I want printed
• Logging messages go to stderr

Usage

Here's the script in action:

$ ./log_example
2019-01-18 08:26:31,929 WARNING ./log_example:16 This is a warning message
2019-01-18 08:26:31,929 ERROR ./log_example:17 This is an error message
2019-01-18 08:26:31,929 CRITICAL ./log_example:18 This is a fatal/critical message
$ ./log_example -v
2019-01-18 08:26:33,893 INFO ./log_example:15 This is an informational message
2019-01-18 08:26:33,893 WARNING ./log_example:16 This is a warning message
2019-01-18 08:26:33,893 ERROR ./log_example:17 This is an error message
2019-01-18 08:26:33,894 CRITICAL ./log_example:18 This is a fatal/critical message
$ ./log_example -vv
2019-01-18 08:26:35,603 DEBUG ./log_example:14 This is a debugging message
2019-01-18 08:26:35,603 INFO ./log_example:15 This is an informational message
2019-01-18 08:26:35,603 WARNING ./log_example:16 This is a warning message
2019-01-18 08:26:35,603 ERROR ./log_example:17 This is an error message
2019-01-18 08:26:35,603 CRITICAL ./log_example:18 This is a fatal/critical message
$ ./log_example -vvvvvvvvv
2019-01-18 08:26:38,438 DEBUG ./log_example:14 This is a debugging message
2019-01-18 08:26:38,438 INFO ./log_example:15 This is an informational message
2019-01-18 08:26:38,438 WARNING ./log_example:16 This is a warning message
2019-01-18 08:26:38,438 ERROR ./log_example:17 This is an error message
2019-01-18 08:26:38,438 CRITICAL ./log_example:18 This is a fatal/critical message
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