Constants (Python Convention)0%
Data Types Overview

Constants (Python Convention)

Beginner7 min read•Updated: 2026-09-03
Study Materials

Constants (Python Convention)

Constants represent fixed values that should never be altered throughout program execution.

Key Concepts & Detailed Explanation

While languages like C++ or JavaScript provide 'const', Python relies on naming conventions:

  • Use ALL_CAPS_WITH_UNDERSCORES to signal to developers that a value must not be altered.
  • From Python 3.8+, you can import 'Final' from 'typing' so that static linters (like MyPy or Pylance) highlight accidental modifications.

Code Examples & Output

Python
from typing import Final
 
# Conventional constants
MAX_USERS = 500
TAX_RATE: Final = 0.18
 
# Linters will flag reassignment
print(f"Max Users: {MAX_USERS}, Tax: {TAX_RATE * 100}%")

Expected Output:

Output
Max Users: 500, Tax: 18.0%

Best Practices & Common Pitfalls

Define global constants in a dedicated 'config.py' or 'constants.py' file for large projects.

Practice Quiz

1. What naming style indicates a constant in Python?

  • A) camelCase
  • B) ALL_CAPS
  • C) snake_case
  • D) lowercase
Answer: B Explanation: ALL_CAPS is the PEP 8 convention for constants.

2. Which module provides the 'Final' type annotation to guard constants?

  • A) constants
  • B) typing
  • C) sys
  • D) math
Answer: B Explanation: typing.Final informs type checkers of constant variables.

Practice Challenge

Create a configuration dictionary with constants for DB_HOST, DB_PORT, and MAX_RETRIES.

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