Logging in Python: How to Implement a Robust Logging System for Your Applications

Logging in Python: How to Implement a Robust Logging System for Your Applications

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Vikram Singh
Assistant Manager - Content
Updated on Apr 6, 2023 09:20 IST

Learn about logging in Python, a crucial tool for software development. Understand the built-in logging module, logging levels, configuring logging, and best practices for writing effective and efficient logs. Implement a robust logging system to diagnose issues, monitor performance, and improve the overall quality of your Python applications.


Table of Content

Introduction to Logging

What is Logging?

Logging is the process of recording events and messages generated by an application during its execution. These logs provide valuable information about the application’s behavior and can help developers troubleshoot issues and improve the overall quality of the software.

Why is it important for software development?

Logging is important for software development for several reasons:

  • Debugging: Logs identify and troubleshoot errors, bugs, and other issues in the application. By examining the logs, developers can gain insight into what went wrong, when it happened, and under what circumstances.
  • Performance Monitoring: Logs can also monitor the performance of an application, including response times, server load, and other metrics. It helps developers identify bottlenecks and optimize the application for better performance.
  • Auditing and Compliance: Many applications require maintaining logs for compliance or auditing purposes. These logs provide a record of all the application’s actions and can be used to verify that it is functioning correctly and within legal and regulatory guidelines.
  • Maintenance and Support: Logs support staff to diagnose and resolve issues reported by users. By examining the logs, support staff can identify the cause of the problem and provide a solution or workaround.
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What are the different logging modules in Python?

The logging module is a built-in module in Python that provides a flexible and powerful application logging system. It defines several classes and methods that create and manage logs in Python.

Here’s an overview of the key classes and methods in the logging module:

  • Logger
    • The Logger class is the main class in the logging module. It creates loggers that record messages from different parts of the application. 
    • Loggers can be hierarchical, meaning messages sent to a parent logger will also be sent to its child loggers.
  • Handler 
    • The Handler class specifies how to handle log messages. 
    • It sends messages to different destinations, such as a file, console, or email. 
      • Multiple handlers can be added to a logger to handle messages differently.
  • Formatter
    • It specifies the format of log messages.
    • It includes information such as the time stamp, logger name, message level, and message text.
  • Filter
    • It specifies which log messages should be processed by a handler.  
    • It filters messages based on their level, logger name, or other criteria.
  • LogRecord
    • It represents a single log message. 
    • It contains information such as the message level, logger name, time stamp, and message text.

Some of the key methods in the logging module include:

  • getLogger(name): Creates and returns a logger object with the specified name.
  • setLevel(level): Sets the minimum logging level for the logger and its handlers.
  • addHandler(handler): Adds a handler to the logger to handle log messages.
  • setFormatter(formatter): Sets the format for the logger and its handlers.
  • debug(msg), info(msg), warning(msg), error(msg), critical(msg): These methods use log messages at different levels of severity.

What are the different Logging Levels in Python?

The logging module in Python provides five different levels of logging, each with a specific purpose and use case. Here’s an overview of the different logging levels and when to use them:


  • It is the lowest logging level used for detailed diagnostic information. 
  • This level is typically used during development and debugging to provide information about the application’s inner workings. 
  • It should be used sparingly in production environments, as it can generate a large volume of logs.


  • The INFO level provides general information about the application’s operation. 
  • This level is typically used for logging important events, such as application startup and shutdown, as well as major application milestones.
  •  INFO logs are useful for monitoring an application’s overall health and behavior.


  • The WARNING level indicates a potential problem or issue in the application. 
  • This level is typically used for logging events that are not critical but may require attention, such as deprecated function usage or a configuration issue. 
  • WARNING logs are useful for identifying potential problems before they become critical.


  • The ERROR level indicates a critical error or exception in the application. 
  • This level is typically used for logging events that indicate a failure in the application, such as an unhandled exception or a database connection failure. 
  • ERROR logs are useful for troubleshooting and identifying the cause of application failures.


  • The CRITICAL level is the highest logging level and indicates a fatal error in the application. 
  • This level is typically used for logging events that indicate a complete failure of the application, such as a system crash or data corruption. 
  • CRITICAL logs are useful for identifying and resolving issues that can cause serious damage or data loss.

How to set up logging configuration for your Python Application?

Configuring logging in Python involves setting up loggers, handlers, and formatters to define how log messages should be processed and formatted. Here’s a step-by-step guide on how to set up logging configuration for your Python application:

  • Import the logging module: The first step is to import the logging module into your Python script or module.
import logging
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  • Create a logger object: The next step is to create a logger object using the getLogger() method. The name parameter is optional and can give the logger a specific name. If no name is provided, the root logger will be used.
logger = logging.getLogger('my_logger')
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  • Set the logging level: Use the setLevel() method to set the minimum logging level for the logger. This will determine which log the logger and its handlers process messages.
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  • Create a handler object: Handlers specify how to handle log messages. Use the desired handler class to create a handler object. For example, to log messages to a file, use the FileHandler class.
file_handler = logging.FileHandler('my_app.log')
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  • Set the handler level: Use the setLevel() method to set the minimum logging level for the handler. This will determine which log the handler processes messages.
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  • Create a formatter object: Formatters specify the format of log messages. Use the Formatter class to create a formatter object. The format string can include placeholders for attributes such as the log message, timestamp, and logger name.
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
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  • Set the formatter for the handler: Use the setFormatter() method to set the formatter. This will format log messages using the specified format string.
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  • Add the handler to the logger: Use the addHandler() method to add the handler. This will cause log messages to be processed by the handler.
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  • Log messages: Use the logging methods such as debug(), info(), warning(), error(), and critical() to log messages at the desired logging level.
logger.info('Application started')
logger.debug('Debugging information')
logger.warning('Config file not found')
logger.error('Database connection failed')
logger.critical('System failure')
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Tips and tricks for writing effective and efficient logs

Here are some logging best practices for writing effective and efficient logs in Python:

  • Log exceptions and tracebacks: Whenever an exception occurs, log the exception traceback to help diagnose the issue. You can use logging.exception() method to automatically log the traceback.
# Some code that might raise an exception
except Exception as e:
logging.exception('An error occurred: %s', e)
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  • Use contextual information: In addition to the log message, include contextual information such as the name of the function or method is executed, the current user, or any relevant IDs or metadata. You can use the logging extra parameter to add extra information to log records.
logging.info('User %s logged in', user, extra={'user_id': user_id})
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  • Avoid excessive logging: Be careful not to log too much information, especially in production environments. Excessive logging can slow down your application and consume a lot of disk space. Use the appropriate logging level for each message to keep the log output concise.
  • Use structured logging: Structured logging allows you to log data in a structured format, which makes it easier to search, filter, and analyze log data. You can use a JSON or YAML formatter to log-structured data.
  • Use log rotation: When logging into files, implement log rotation to prevent log files from growing too large. You can use the RotatingFileHandler or TimedRotatingFileHandler classes to rotate log files automatically.
  • Use a logging library: Instead of using print statements for debugging, use a logging library. A logging library provides more flexibility and control over logging output and allows you to switch between different logging backends easily.
  • Configure logging in a separate module: Avoid configuring logging in your application code. Instead, create a separate module or configuration file for logging configuration, and import it into your application code.


In conclusion, logging is an essential tool for software development, helping developers diagnose issues and monitor application performance. The built-in logging module in Python provides a flexible and powerful logging system that can be easily customized and configured to meet your needs.

About the Author
Vikram Singh
Assistant Manager - Content

Vikram has a Postgraduate degree in Applied Mathematics, with a keen interest in Data Science and Machine Learning. He has experience of 2+ years in content creation in Mathematics, Statistics, Data Science, and Mac... Read Full Bio