Python logging is an essential part of building software, a powerful language feature for logging different events and errors. Python provides a logging module that gives us fine-grained control over how log messages are handled. It also allows us to set levels to identify critical messages and filter them out more flexibly. This python logging tutorial will introduce you to the logging module and help you use it to filter out messages that you don't want to see when developing.

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What Is Python Logging?

Python logging is a module that allows you to track events that occur while your program is running. You can use logging to record information about errors, warnings, and other events that occur during program execution. And logging is a useful tool for debugging, troubleshooting, and monitoring your program.

How Does Logging in Python Work?

Python import logging is a powerful tool for debugging and troubleshooting code. By default, Python will log all messages to the standard output stream. However, it is also possible to configure Python to log messages to a file, or even to a remote server.

There are three steps to configuring Python logging:

  • Choose a logger - This is where the object that will actually do the logging.
  • Configure the logger - This step involves telling the logger to log messages, what format to use, and what level of detail to include.
  • Use the logger - This step simply involves using the logger object in your code to log messages.

Python Logging Level

Python logging levels are used to indicate the severity of a message. There are five logging levels in Python: 

  • DEBUG, 
  • INFO, 
  • WARNING, 
  • ERROR, 
  • And CRITICAL. 
  • WARNING is a default stage, meaning only messages with a group of WARNING or higher will be logged. 
  • You can change the logging level to DEBUG to see all messages or to ERROR to only see notes with a level of ERROR or higher.

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The Basics

The basicConfig() method can be used to configure the logging system in a number of ways. By default, it will configure the logger to output to the standard output stream, with a default logging level of INFO. However, you can use the keyword arguments to specify different output streams and logging levels. 

For example, you could use the following to configure the logger to output to a file with a logging level of DEBUG:

logging.basicConfig(filename='example.log', level=logging.DEBUG)

There are a variety of parameters that can be used with the basicConfig() function in Python. 

Some of the Most Commonly Used Parameters are the Following:

  • filename: This parameter is used to specify the filename that the logging messages will be written to.
  • filemode: This parameter is used to specify the mode that the file will be opened. The default mode is 'a', which means that messages will be appended to the end of the file.
  • Format: This parameter is used to specify the format of the logging messages. The default format is '%(levelname)s: %(message)s', which means that the level name and message will be printed.
  • datefmt: This parameter is used to specify the date format of the logging messages. 
  • Level: This parameter is used to specify the minimum level of messages that will be logged. The default level is 'WARNING', which means that only messages with a level of 'WARNING' or higher will be logged.

The Logging Module

Python's logging module provides a powerful and flexible way to log messages from your Python code. You can use the logging module to log messages to a file, to the python logging console, or to a custom logging handler.

  • The logging module has a number of different logging levels, which allow you to control the amount of detail that is logged. 
  • For example, you can use the logging module to log only errors, or to log everything from debug messages to critical errors.
  • You can also use the logging module to format your log messages in a variety of ways. 
  • For example, you can include the timestamp, the logger name, or other information in the log message.
  • The logging module is highly configurable, and you can use it to create custom logging handlers to meet your specific needs.

Configurations [Basic and Advance]

There are two types of logging configurations: basic and advanced. Basic logging configuration is sufficient for most purposes, but advanced logging configuration provides more options and flexibility. 

  • Basic logging configuration is typically used for troubleshooting purposes and consists of setting the log level and output destination. The log level determines the amount and type of information written in the log file. The output destination specifies where the log file is located. 
  • Advanced logging configuration allows you to select additional options, such as the log file format and the rotation schedule. The advanced log file format can be text, XML, or JSON.

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Formatting

To format the logging output, you must use a particular library such as "log4j". This library provides several ways to format the output of your logging statements. 

For example, you can specify the minimum level of severity that should be logged, the output format (including date and time), and where the output should be sent (e.g., to a file, to the python logging console, or to a remote server). 

Logging Variable Data

Variable data logging is an essential process in many scientific and engineering disciplines. By recording data over time, researchers can track the progress of a system or method and identify any trends or changes. Logging data can also help debug purposes and allow engineers to identify and fix any issues that may arise. 

There are many ways to log variable data. 

  • One standard method is to use a data logger, a device that can be attached to a system or process to record data automatically over time. Data loggers typically have various input options tailored to a given application's specific needs.
  • Another option for logging variable data is to use a software application. Many software programs available can be used for data logging; each has advantages and disadvantages. Some software programs are designed specifically for data logging, while others may have data logging capabilities as part of a more extensive suite of tools.

No matter what method is used, it is crucial to choose a data logging system that is reliable and accurate.

Capturing Stack Traces

A stack trace is a report of the active stack frames at a certain point during the execution of a program. With the help of stack trace, we can determine where the program was when it crashed, and stack trace can be used to trace the path of execution through the program. And there are a few ways to capture stack traces. 

  • The most common way is to use a debugger. A debugger is a program that steps through code, examines variables, and sets breakpoints. When a breakpoint is reached, the debugger will stop execution and print out the current stack trace.
  • Another way to capture stack traces is to use a logging framework. 

Classes and Functions

There are two main types of logging in Python, and those are class-based logging and function-based logging.

  • Class-based logging is the most common type of logging in Python. It allows you to define a class representing a logger and then instantiate it to create a logger object. You can then use the logger object to log messages.
  • Function-based logging is less common but can be helpful in certain situations. With function-based logging, you define a function representing a logger and then call that function to log messages.

The most commonly used classes defined in the logging module are the following:

  • Logger: This is the class that is used to create loggers. A logger is an object that is used for logging messages.
  • Handler: This is the class that is used to create handlers. A handler is an object that is used to handle logging messages.
  • Filter: This is the class that is used to create filters. A filter is an object that is used to filter logging messages.
  • Formatter: This is the class that is used to create formatters. A formatter is an object that is used to format logging messages.

Handlers

Handlers are essential to any logging system, allowing you to route log messages to different destinations according to your needs. Common goals for log messages include files, streams, and email addresses. By using handlers, you can ensure that your log messages are always delivered to the right place.

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Examples

There are a few different ways to use logging in Python, and for example:

  • The most basic logging method is to print messages to the python logging console. This console is excellent for simple debugging, but it can get messy if you publish many messages. To use this method, you can use the print() function.
  • You can use the logging module if you want more control over your logging. This module provides many features, such as logging into a file or sending emails when certain events happen. To use this module, you must create a logger object and then call the various methods on that object.
  • There are also a few third-party logging modules that provide additional features. One popular module is called "logbook", which offers many handy features, such as the ability to format your logs differently.

Regardless of your chosen method, logging can be a helpful tool for debugging your code and keeping track of what's happening in your application.

Python Logging to File

Python logging to files is a handy tool. It allows you to keep track of your Python scripts and programs and to see what is happening in them. This tool can be beneficial when debugging or troubleshooting.

How to Create?

  • You first need to create a logger to use Python import logging to file. 
  • This logger is done using the logging.getLogger() function.
  • Once you have a logger, you can log messages to a file using the logger.log() function.

Python logging to files is exceptionally flexible. You can configure the logger to output multiple files and rotate them to stay manageable. You can also add filters to the logger so that only specific messages are logged.

You're missing out on a valuable tool if you need to use Python logging to file.

Benefits of Logging in Python

  • Python logging is a powerful tool that can help you debug your code and track errors. When used correctly, it can provide valuable insights into what your code is doing and where it is failing. 
  • And logging can be used to monitor your code's performance and identify potential bottlenecks. 

Overall, python logging is a valuable tool that every python developer should be familiar with.

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Conclusion

So let's conclude that logging is a very important part of any software or any programming language. Logging can help you understand what your program did, what went wrong, and how to fix it. So, it is mandatory to know the logging if you are a python developer. You can use logging when testing and debugging your program. So, if you have started logging in yet, it is the perfect time to begin your journey with Python.

If you are looking to enhance your Python programming skills, we would suggest you check out Simplilearn’s Python Certification Course. If you are looking to progress further with your software development skills, we would highly recommend you check Post Graduate Program in Full Stack Web Development. This course, designed in collaboration with Caltech CTME, can help you hone the right skills and make you job-ready.

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