how to use loggings in python to debug

A common way of debug during programming is to print() information at critical checkpoints in the program. But sometimes, you’ll get tired of endless verbose console outputs… So here’s a solution

use logging

Logging is a means of tracking events that happen when some software runs. The software’s developer adds logging calls to their code to indicate that certain events have occurred.

…Events also have an importance which the developer ascribes to the event; the importance can also be called the level or severity.

print, but with levels:

import logging
logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s [%(levelname)s] %(message)s')

By configuring the level parameters, one is essentially setting a threshold of message to print:

save loggings to file

import logging
logging.basicConfig(filename='example.log',
                    encoding='utf-8',
                    level=logging.DEBUG, 
                    format='%(asctime)s [%(levelname)s] %(message)s',
                    filemode='a' # 'a' for append, 'w' for overwrite
                   )

example usage:

logging.debug('This message should go to the log file')
logging.info('So should this')
logging.warning('And this, too')
logging.error('And non-ASCII stuff, too, like Øresund and Malmö')

advanced: customize logger:

One can instantiate a customized Logger calss by calling logging.getLogger() function and providing a name. A good practice is to pass __name__ as the name parameter:

import logging
logger = logging.getLogger(__name__)
logger.warning("Look at my logger!")

To configuring self-initiated logger, calling basicConfig won’t work. Instead, handlers and formatters need to be used.

This would be another story! Here’s a helpful link for more detail: Creating a Custom Logger.

Actually, I somehow suggest consulting an LLMs to do the job🤪.

set threshold on command-line:

python logging_demo.py --log=INFO

reference

Logging HOWTO by Vinay Sajip.