Constants
- Python course
- Intermediate
- Lesson 28/116
- 4 min
Learn class-level constants.
Class constants
A constant is a value that does not change. In Python constants are named in uppercase: MAX_USERS = 100. When defined in a class body, it becomes a class constant.
Example: class Config:\n MAX_USERS = 100\n DEFAULT_LANG = "en". Accessed as Config.MAX_USERS. Python constants can technically be changed, but the uppercase name signals that you should not. This is a convention.
Using constants
Constants remove magic numbers. Writing if users > Config.MAX_USERS is more readable than if users > 100; the meaning of the number is in its name.
Class constants are accessed via the class: Config.MAX_USERS, Config.DEFAULT_LANG. They can be accessed via an instance too, but the class name is more common. When the value changes, you update it in one place; this eases maintenance.
Practice Define the Config constants
Define a class named Config. Add the constants MAX_USERS = 100 and DEFAULT_LANG = "en" in the body. Then call print(Config.MAX_USERS) and print(Config.DEFAULT_LANG).
Starter code
# Define the Config classSample solution
# Define the Config class
class Config:
MAX_USERS = 100
DEFAULT_LANG = "en"
print(Config.MAX_USERS)
print(Config.DEFAULT_LANG)Expected output
100 en
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the constant concepts
| Term | Meaning |
|---|---|
MAX_USERS |
Uppercase name |
100 |
Constant value |
Config.MAX_USERS |
Access via class |
2 How is a class constant named?
- lowercase
- camelCase
- UPPER_SNAKE_CASE Correct answer
- PascalCase
Explanation: Constants use uppercase letters and underscores.
3 Complete the constant declaration
class Config:
____ = 100class Config:
MAX_USERS = 100Explanation: Constants use uppercase letters and underscores.