PythonHow-ToBeginner · 3 min read

How to Use Logging Module in Python: Simple Guide

Use the logging module in Python by importing it and calling functions like logging.debug(), logging.info(), or logging.error() to record messages. Configure logging with logging.basicConfig() to set the output format and level.

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Syntax

The logging module provides functions to log messages at different levels. You start by importing the module, then configure it using logging.basicConfig(). After that, use functions like logging.debug(), logging.info(), logging.warning(), logging.error(), and logging.critical() to log messages.

The basicConfig function lets you set the minimum level of messages to show and the format of the log output.

python

import logging

logging.basicConfig(level=logging.INFO, format='%(levelname)s:%(message)s')

logging.debug('This is a debug message')
logging.info('This is an info message')
logging.warning('This is a warning message')
logging.error('This is an error message')
logging.critical('This is a critical message')

Output

INFO:This is an info message WARNING:This is a warning message ERROR:This is an error message CRITICAL:This is a critical message

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Example

This example shows how to set up logging to print messages to the console with a simple format. It demonstrates logging messages of different severity levels. Only messages at or above the set level (INFO) are shown.

python

import logging

# Set up logging to show INFO and above messages
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s')

logging.debug('Debug message - not shown')
logging.info('Info message - shown')
logging.warning('Warning message - shown')
logging.error('Error message - shown')
logging.critical('Critical message - shown')

Output

2024-06-01 00:00:00,000 - INFO - Info message - shown 2024-06-01 00:00:00,000 - WARNING - Warning message - shown 2024-06-01 00:00:00,000 - ERROR - Error message - shown 2024-06-01 00:00:00,000 - CRITICAL - Critical message - shown

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Common Pitfalls

One common mistake is calling logging.basicConfig() multiple times; it only works once per program run. Another is not setting the logging level, which defaults to WARNING and hides DEBUG and INFO messages. Also, using print statements instead of logging loses the benefits of log levels and formatting.

Always configure logging once at the start of your program.

python

import logging

# Wrong: calling basicConfig twice does nothing the second time
logging.basicConfig(level=logging.DEBUG)
logging.basicConfig(level=logging.ERROR)  # This call is ignored

logging.info('This info message will show because level is DEBUG')
logging.error('This error message will also show')

Output

INFO:root:This info message will show because level is DEBUG ERROR:root:This error message will also show

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Quick Reference

Function	Description
logging.debug(msg)	Logs a message with DEBUG level (lowest priority)
logging.info(msg)	Logs a message with INFO level
logging.warning(msg)	Logs a message with WARNING level
logging.error(msg)	Logs a message with ERROR level
logging.critical(msg)	Logs a message with CRITICAL level (highest priority)
logging.basicConfig()	Configures the logging system (level, format, output)

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Key Takeaways

Import the logging module and configure it once using logging.basicConfig().

Use different logging functions to record messages by importance level.

Set the logging level to control which messages appear (DEBUG, INFO, WARNING, ERROR, CRITICAL).

Avoid calling basicConfig multiple times; it only works once per program run.

Logging provides better control and formatting than print statements for tracking program events.