Minimum knowledge to get started with the Python logging module

Minimum knowledge to get started with the Python logging module

This article will show you how to get started with the Python logging module for app development with minimal knowledge. Since we have compiled only the minimum knowledge that can be used immediately in development, we hope that you can use it as a starting point while supplementing the missing information.

Basic functions of logging

It's like a print statement (but don't use it this way as logging doesn't make sense)

import logging
logging.warning（ 'Watch out！') # Print a message to the console
logging.info（ 'I said so') # The default log level is a warning, so nothing should be output to the console

Minimum knowledge and settings to use logging in app development

logger

• logger object

• Set the logger to use

• Set log level (DEBUG, WARNING, etc.)

• Decide whether to send the log to the console or a file (use handlers such as StreamHandler, TimedRotatingFileHandler)

• logger = logging.getLogger（ 'app'）

• Build a logger object

• The logger is named app

Templates for using logging

• This example assumes you have two files like this:

root
├──your_app.py
├──logging.conf
└──logging_dev.conf

• Ideally, these conf files should probably be set to a different directory, such as:

root
├──app
│└──your_app.py
└──conf
    ├──logging.conf
    └──logging_dev.conf

• You can use the following template to perform logging in your development environment and use it in combination with the following conf file examples.

your_app.py

import logging

# read the conf file
logging.config.fileConfig('logging_dev.conf', disable_existing_loggers=False)

# create logger
logger = logging.getLogger('app')

def main():
    try:
        1/0  # ZeroDivisionError
        # your code goes here   
    except Exception as e:
        logger.exception(e.args)


if __name__ == '__main__':
    main()

logging config file

point

• Set the log level appropriately for both dev and production.
• The file handler must be selected between RotatingFileHandler and TimedRotatingFileHandler.

Sample operation configuration file (Note that the log level is INFO)

logging-prod.conf

[loggers]
keys=root,app

[formatters]
keys=default

[handlers]
keys=frotate,default

[formatter_default]
format=%(asctime)s %(levelname)s %(message)s
datefmt=%Y/%m/%d %H:%M:%S

[handler_frotate]
class=handlers.TimedRotatingFileHandler
formatter=default
args=('logs/logger.log', 'W0', 1, 100)

[handler_default]
class=StreamHandler
formatter=default
args=(sys.stdout,)

[logger_app]
level=INFO
handlers=frotate
qualname=app

[logger_root]
level=INFO
handlers=default

Sample dev config file (note that the log level is NOTSET and is noisier than DEBUG)

logging-dev.conf

[loggers]
keys=root,app

[formatters]
keys=default

[handlers]
keys=frotate,default

[formatter_default]
format=%(asctime)s %(levelname)s %(message)s
datefmt=%Y/%m/%d %H:%M:%S

[handler_frotate]
class=handlers.TimedRotatingFileHandler
formatter=default
args=('logs/logger_dev.log', 'W0', 1, 100)

[handler_default]
class=StreamHandler
formatter=default
args=(sys.stdout,)

[logger_app]
level=NOTSET
handlers=frotate
qualname=app

[logger_root]
level=NOTSET
handlers=default

Summary

I have briefly introduced the minimum usage of the logging module. If you need to know more details, please take a look at the documents introduced in [Reference](see #).

reference

• Logging configuration
• Logging How To
• Good logging practice in Python
• Notes on learning about Python logging
• Notes on reading logging settings from a file