CHAPTER 8 — Variables & Naming Rules

CHAPTER 8 — Variables & Naming Rules - Printable Version

+- The Lumin Archive (https://theluminarchive.co.uk)
+-- Forum: The Lumin Archive — Core Forums (https://theluminarchive.co.uk/forumdisplay.php?fid=3)
+--- Forum: Courses — Structured Learning (https://theluminarchive.co.uk/forumdisplay.php?fid=69)
+---- Forum: Beginner’s Guide to Coding — Python From Zero to Skill (https://theluminarchive.co.uk/forumdisplay.php?fid=72)
+---- Thread: CHAPTER 8 — Variables & Naming Rules (/showthread.php?tid=226)

CHAPTER 8 — Variables & Naming Rules - Leejohnston - 11-15-2025

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

---

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.

---

8.2 Creating Variables

Just use:

Code:
variable_name = value

Examples:

Code:
score = 0

player = "Alex"

temperature = 18.5

is_logged_in = True

---

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

---

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.

---

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.

---

8.6 Overwriting Variables

A variable stores *the latest* value assigned:

Code:
score = 10

score = 20

print(score)

Output:

Code:
20

---

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: "))

---

8.8 Combining Variables

Examples:

Code:
first = "Lee"

last = "Johnston"

full_name = first + " " + last

Output:

Code:
Lee Johnston

---

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

---

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

---

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

---

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.

---

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