131.3 Constants and naming conventions

Learn how to define values that do not change, and how to name variables consistently for readable, maintainable code.

What is a constant?

A constant is a value that does not change while the program runs. Using constants makes code more readable, easier to maintain, and helps prevent accidental changes to important values.

Constants are often used for:

• Screen dimensions

• Player speed

• Configuration values

• Limits or thresholds

Declaring constants

Python does not have true constants, but programmers use uppercase variable names to signal that a value should not be changed.

Pseudocode

SET SCREEN_WIDTH TO 800
SET SCREEN_HEIGHT TO 600
SET MAX_HEALTH TO 100

Python

SCREEN_WIDTH = 800
SCREEN_HEIGHT = 600
MAX_HEALTH = 100

Even though Python doesn’t enforce it, treating these as fixed values is part of good practice.

Why use constants?

In this example below, the player width should always be half the screen width.

Without constants:

player_x = 400
screen_width = 400  # Mistake! Should be 800, but the value was reused incorrectly

With constants:

player_x = SCREEN_WIDTH // 2

Benefits:

• Makes code self-documenting

• Reduces “magic numbers” (unexplained hard-coded values)

• Simplifies future updates — just change the constant in one place

Naming conventions

To keep code readable, follow these standard naming styles:

• Constants: ALL_CAPS with underscores Example: MAX_SPEED, DEFAULT_FONT_SIZE

• Variables (Python): snake_case Example: user_score, player_position

• Class names (Python): CamelCase Example: GameScreen, PlayerStats

• Booleans: Use names that start with is_, has_, or can_ Example: is_visible, has_lives_left, can_jump

Reserved words

Avoid using keywords reserved by the programming language. These include:

• if, else, for, while

• class, def, True, False

These words have special meanings and will cause syntax errors if used as variable names.

Key concepts

• A constant is a named value that does not change during execution.

• Using named constants improves clarity and maintainability.

• Naming conventions help make code consistent and professional.

• Reserved words should not be used as variable names.