Master Python Variables: Definitions, Naming Rules, and Best Practices

Variables represent quantities that can change; they record the state of real-world objects so a computer can recognize them.

1. What is a variable?

A variable is a quantity that can vary. It records a state of the real world, enabling the computer to recognize objects similarly to how humans do.

Quantity: records real-world state for computer recognition.

Change: real-world states can change over time.

2. Why do we need variables?

Variables are needed to describe the ever‑changing states in both the real world and program execution, such as a game character’s level increasing from 0 to 30.

3. Defining variables in Python

In Python, variables are created by assigning a value to a name.

name = 'nick'
age = 19
gender = 'male'
height = 180
weight = 140

4. Components of a variable

A Python variable consists of three parts:

Variable name – used to reference the stored value.

Assignment operator – the equals sign (=).

Variable value – the data representing a state.

name  # error, no value assigned
age = 18
height = 185
print(age)   # 18
print(height)   # 185

5. Naming conventions

Good variable names should be descriptive, use only letters, numbers, and underscores, start with a letter or underscore, and avoid Python keywords.

and, as, assert, break, class, continue, def, del, elif, else, except,
exec, finally, for, from, global, if, import, in, is, lambda, not,
or, pass, print, raise, return, try, while, with, yield

6. Variable naming styles

Two common styles are camelCase and snake_case, with snake_case recommended.

# camelCase
AgeOfNick = 19
print(AgeOfNick)

# snake_case
age_of_nick = 19
print(age_of_nick)

7. Constants

Constants are values that should not change. Python has no dedicated syntax, so the convention is to use all‑uppercase names. They can still be reassigned, but it is discouraged.

AGE_OF_NICK = 19
print(AGE_OF_NICK)   # 19
AGE_OF_NICK = AGE_OF_NICK + 1
print(AGE_OF_NICK)   # 20