Logging in Python

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July 22, 2024
Logging in Python
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Recording relevant information during the execution of your program is a good practice as a Python developer when you want to gain a better understanding of your code. This practice is called logging, and it’s a very useful tool for your programmer’s toolbox. It can help you discover scenarios that you might not have thought of while developing.

These records are called logs, and they can serve as an extra set of eyes that are constantly looking at your application’s flow. Logs can store information, like which user or IP accessed the application. If an error occurs, then logs may provide more insights than a stack trace by telling you the state of the program before the error and the line of code where it occurred.

Python provides a logging system as part of its standard library. You can add logging to your application with just a few lines of code.

In this tutorial, you’ll learn how to:

  • Work with Python’s logging module
  • Set up a basic logging configuration
  • Leverage log levels
  • Style your log messages with formatters
  • Redirect log records with handlers
  • Define logging rules with filters

When you log useful data from the right places, you can debug errors, analyze the application’s performance to plan for scaling, or look at usage patterns to plan for marketing.

You’ll do the coding for this tutorial in the Python standard REPL. If you prefer Python files, then you’ll find a full logging example as a script in the materials of this tutorial. You can download this script by clicking the link below:

Take the Quiz: Test your knowledge with our interactive “Logging in Python” quiz. You’ll receive a score upon completion to help you track your learning progress:

Logging in Python

Interactive Quiz

Logging in Python

In this quiz, you'll test your understanding of Python's logging module. With this knowledge, you'll be able to add logging to your applications, which can help you debug errors and analyze performance.

If you commonly use Python’s print() function to get information about the flow of your programs, then logging is the natural next step for you. This tutorial will guide you through creating your first logs and show you how to make logging grow with your projects.

Starting With Python’s Logging Module

The logging module in Python’s standard library is a ready-to-use, powerful module that’s designed to meet the needs of beginners as well as enterprise teams.

The main component of the logging module is something called the logger. You can think of the logger as a reporter in your code that decides what to record, at what level of detail, and where to store or send these records.

Exploring the Root Logger

To get a first impression of how the logging module and a logger work, open the Python standard REPL and enter the code below:

Python 
>>> import logging
>>> logging.warning("Remain calm!")
WARNING:root:Remain calm!

The output shows the severity level before each message along with root, which is the name the logging module gives to its default logger. This output shows the default format that can be configured to include things like a timestamp or other details.

In the example above, you’re sending a message on the root logger. The log level of the message is WARNING. Log levels are an important aspect of logging. By default, there are five standard levels indicating the severity of events. Each has a corresponding function that can be used to log events at that level of severity.

Here are the five default log levels, in order of increasing severity:

Log Level Function Description
DEBUG logging.debug() Provides detailed information that’s valuable to you as a developer.
INFO logging.info() Provides general information about what’s going on with your program.
WARNING logging.warning() Indicates that there’s something you should look into.
ERROR logging.error() Alerts you to an unexpected problem that’s occured in your program.
CRITICAL logging.critical() Tells you that a serious error has occurred and may have crashed your app.

The logging module provides you with a default logger that allows you to get started with logging without needing to do much configuration. However, the logging functions listed in the table above reveal a quirk that you may not expect:

Python 
>>> logging.debug("This is a debug message")

>>> logging.info("This is an info message")

>>> logging.warning("This is a warning message")
WARNING:root:This is a warning message

>>> logging.error("This is an error message")
ERROR:root:This is an error message

>>> logging.critical("This is a critical message")
CRITICAL:root:This is a critical message

Notice that the debug() and info() messages didn’t get logged. This is because, by default, the logging module logs the messages with a severity level of WARNING or above. You can change that by configuring the logging module to log events of all levels.

Read the full article at https://realpython.com/python-logging/ »

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July 22, 2024 at 07:30PM
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