[Leejohnston]

Chapter 8 — Variables & Naming Rules
How programmers store information and write clean, readable code

A variable is a “box” in memory where Python stores a value.
You choose the name, and Python remembers the value.

Example:

Code:

name = "Mia"
age = 14
height = 1.62

Python now remembers:
• name → "Mia" 
• age → 14 
• height → 1.62 

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8.1 Why Variables Matter

Variables allow you to:

• store user input 
• reuse values 
• change values later 
• perform calculations 
• make programs dynamic 

Without variables, everything would be hard-coded and static.

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8.2 Creating Variables

Just use:

Code:

variable_name = value

Examples:

Code:

score = 0
player = "Alex"
temperature = 18.5
is_logged_in = True

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8.3 Naming Rules (Essential!)

Python variable names:

✔ must start with a letter or underscore 
✔ may contain letters, numbers, and underscores 
✔ are case-sensitive (age ≠ Age ≠ AGE) 
✔ should be descriptive 

❌ Not allowed:

Code:

2name
user-name
total value

✔ Allowed:

Code:

name2
user_name
total_value

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8.4 The Professional Naming Style

Python developers use:

snake_case → all lowercase, words separated by underscores.

Examples:

Code:

max_speed
user_choice
total_cost
gravity_force

Avoid one-letter names except in maths loops.

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8.5 Dynamic Typing

In Python, a variable can change type:

Code:

value = 10        # int
value = "hello"  # now a string

This is flexible but can also cause confusion, so beginners should keep variables consistent.

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8.6 Overwriting Variables

A variable stores *the latest* value assigned:

Code:

score = 10
score = 20
print(score)

Output:

Code:

20

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8.7 Input + Variables

Everything from input() arrives as a string:

Code:

age = input("Enter age: ")

Convert if needed:

Code:

age = int(input("Enter age: "))
price = float(input("Enter price: "))

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8.8 Combining Variables

Examples:

Code:

first = "Lee"
last = "Johnston"
full_name = first + " " + last

Output:

Code:

Lee Johnston

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8.9 Reassigning using the Old Value

This is extremely common:

Code:

score = 10
score = score + 5

Short version:

Code:

score += 5

Other shortcuts:

Code:

score -= 2
score *= 3
score /= 4

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8.10 Mini Project — Personal Info Card

Ask the user:

• name 
• age 
• favourite colour 
• hobby 

Then print a formatted “profile card.”

Example:

Code:

Name: Mia
Age: 13
Favourite Colour: Purple
Hobby: Drawing

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8.11 Challenge — The Food Bill

Ask the user:

• food price 
• drink price 
• dessert price 

Then:

• calculate total 
• apply 10% tax 
• output final bill to 2 decimals 

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8.12 Chapter Summary

• variables store values 
• snake_case is the professional naming standard 
• variables must start with letters/underscores 
• input() values must be converted for maths 
• shortcut operators save time 
• variables update to the newest assigned value 

Next:
Chapter 9 — Strings & Text Manipulation

Where beginners learn how to edit text, join text, format text, and build real programs with output that looks professional.

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Written and Compiled by Lee Johnston — Founder of The Lumin Archive