What are constants ?

Constant means such variable in which changes cannot be made. Variables are created in Python and values ​​are stored in variables. We can change the values ​​stored in variables whenever we want, but there are some programs in which we do not want to make changes in the values ​​ stored in variables, hence Constant variables are such variables in which changes cannot be made. Below is a short and simple Python code and its explanation to understand Constant :

main.py 
GRAVITY = 9.8  
COMPANY_NAME = "TechSol"
print("Company Name :", COMPANY_NAME)
print("Earth Gravity :", GRAVITY)

1. GRAVITY and COMPANY_NAME : GRAVITY and COMPANY_NAME are constants because their names are written entirely in uppercase.
2. Fixed Value : 9.8 and "TechSol" are values ​​that will never change during the entire program's execution.
3. Readability : Any other programmer looking at the code will immediately understand that the values ​​of these variables written in uppercase letters are not to be tampered with or changed anywhere in the code.

Rules for Constants

Since Python does not have a built-in const keyword, its rules are entirely based on naming conventions and best practices :
1. Constant names must always be in uppercase letters.
True: TOTAL_LIMIT = 100 , False: Total_Limit = 100
2. 2. If the name contains more than one word, only underscores (_) should be used to join them.
Example: MAX_LOGIN_ATTEMPTS, DATABASE_PASSWORD
3. Like normal identifiers, constant names can never start with a number. They must always start with a letter or an underscore.
True: PORT_8080 = 8080 , False: 8080_PORT = 8080
4. The use of any special characters (e.g. @, $, %, -) other than the underscore (_) in the name is strictly prohibited.
5. As a rule, all constants should always be written at the top of the script/file or in a separate configuration module, not inside a function or loop.

Features Of Constant

1. Improves Readability : Using PI instead of writing 3.14159 repeatedly in the code makes the code much easier to read and understand.
2. Easy Maintenanc : If a fixed value has to be changed in the future (like tax rate increases from 5% to 18%), then you don't have to change it everywhere in the code. You have to change the value of the constant only at one place.
3. Human Discipline Dependent : It is a unique feature of Python that here constants are completely dependent on the mutual agreement and discipline of the developers, because in the background they work just like normal variables.
4. Global Scope Utility : Constants are usually defined at the top of the program or in a separate file (constants.py), so that they can be easily imported anywhere in the entire project.