Skip to content A Comprehensive Guide to Using and Managing Constants

In programming, a constant refers to a name that represents a value that doesn’t change during the program’s execution. Although Python doesn’t have a dedicated syntax for defining constants, they can be implemented using variables that never change their value.

To distinguish constants from other variables, the Python community adopted a naming convention: constant names should be written in uppercase letters. This makes it clear that the variable is intended to hold a constant value and should not be reassigned.

Understanding constants in Python is essential for every Python developer, as they offer several benefits in terms of code readability, reusability, and maintainability.

In this tutorial, you will learn the following:

  • How to properly define constants in Python
  • Identifying built-in constants in Python
  • Using constants to improve code readability, reusability, and maintainability
  • Different approaches to organizing and managing constants in a project
  • Techniques to enforce strict constant behavior in Python

By learning how to define and use constants effectively, you will significantly enhance the readability, maintainability, and reusability of your code.

To make the most of this tutorial, it is recommended to have a basic understanding of Python variables, functions, modules, packages, and namespaces. Additionally, familiarity with object-oriented programming concepts in Python is helpful.

To provide hands-on experience and practical examples, you can download sample code from the link provided. This code demonstrates how to use constants in Python and can be executed to see the concepts in action.

Understanding Constants and Variables

Variables and constants are fundamental concepts in computer programming. They are used to manipulate data and perform operations in a logical and efficient manner.

In any programming project, whether it’s an app, library, or piece of code, variables and constants will undoubtedly be present. Variables are values that can change throughout the program’s execution, while constants hold values that remain fixed.

Defining Your Own Constants in Python

In Python, constants can be defined by following the naming convention of using uppercase letters for the variable name. By adopting this convention, it becomes clear to other developers that the variable is intended to hold a constant value.

There are two main ways to define constants in Python:

  1. User-Defined Constants: These constants are defined by the programmer within the code. They can be used to represent fixed values that are specific to the program’s requirements.

  2. Module-Level Dunder Constants: These constants are defined within a module using double underscore (dunder) names. They are typically used to provide meaningful names for commonly used values within the module.

Putting Constants Into Action

Constants are particularly useful in improving code readability, maintainability, and reusability. By replacing hardcoded values (referred to as “magic numbers”) with named constants, the code becomes easier to understand and modify.

Using constants also promotes code reuse by encapsulating commonly used values in one place. This reduces the chances of errors and makes it easier to update the code in the future.

Another way constants can be utilized is by providing default argument values in functions. This allows for flexibility in function calls while ensuring that a standard value is used when no argument is provided.

Handling Your Constants in a Real-World Project

In real-world projects, it is important to organize and manage constants effectively. This ensures that they are easily accessible, modifiable, and maintainable.

One approach is to group constants together with related code. This improves code organization and makes it easier to understand the purpose of each constant.

In more complex projects, creating a dedicated module for constants is a good practice. This module can be imported as needed in other parts of the project, resulting in cleaner and more modular code.

Constants can also be stored in configuration files, allowing for easy customization without modifying the code. This is particularly useful when deploying the project to different environments or when collaborating with multiple team members.

Handling constants as environment variables is another technique commonly used in real-world projects. This allows for easy configuration and adaptation to different environments without modifying the codebase.

Exploring Other Constants in Python

In addition to user-defined constants, Python provides several built-in constants that can be used in programming. These include constants related to mathematical operations, string handling, and other useful values.

Internal dunder names are special constants in Python that represent certain behaviors or attributes of objects. They are prefixed and suffixed with double underscores, indicating their significance in the Python language.

Useful string and math constants are also available in Python libraries such as the math module. These constants provide predefined values that are commonly used in mathematical calculations and string operations.

Type-Annotating Constants

Annotating constants with types can enhance code understanding and improve type checking. This makes it easier to identify and resolve type-related issues during development.

Defining Strict Constants in Python

Python offers several techniques to enforce strict constant behavior. This ensures that values assigned to constants cannot be modified or reassigned.

Some of these techniques include:

  • The .__slots__ attribute: This limits the attributes that can be assigned to instances of a class, effectively making them constants.

  • The @property decorator: This allows for the creation of read-only properties that act as constants. They cannot be modified once assigned.

  • The namedtuple() factory function: This creates immutable objects with named fields, essentially acting as constants.

  • The @dataclass decorator: This simplifies the creation of classes with read-only attributes, enforcing constant behavior.

  • The .__setattr__() special method: This can be overridden to prevent modifications to the attributes of a class instance, making them constant.


Constants are an important concept in programming, and Python provides various ways to define and utilize them effectively. By using constants, you can improve the readability, maintainability, and reusability of your code.

This tutorial has covered the basics of defining constants in Python, as well as techniques for organizing and managing them in projects. Additionally, it explored other types of constants available in Python and methods for enforcing strict constant behavior.

By mastering the usage of constants, you will enhance your ability to write clean and maintainable code and become a more proficient Python developer.