Making Choices — if / else / elif

By the end of this lesson you can:

• Write an if statement that runs only when a condition is true.
• Add else to handle the "otherwise" path.
• Chain many choices together with elif.

Last lesson, input() let our programs ask the user questions. The reply always landed in a variable as a string — and int() turned numeric answers into real numbers.

Quick puzzle. If Aisyah types 15 when this short program runs, what does it print? What if she types 9?

age = int(input("Your age? "))
if age >= 13:
    print("Welcome to the teens.")
else:
    print("Almost there!")

Part 1 · An everyday decision

Imagine you wake up in Kuala Lumpur. You glance outside.

• If the sky looks dark → bring an umbrella.
• Otherwise → leave it at home.

That's exactly the shape of an if / else in Python. The program checks something, then picks a path.

Part 2 · Comparison operators

Before if, we need a way to compare values. Python has six comparison operators. Each one returns either True or False — a Boolean.

print(5 == 5)
print(5 != 3)
print(7 > 10)
print(7 < 10)
print(8 >= 8)
print(8 <= 7)

Part 3 · The if statement

An if statement runs a block of code only when its condition is true.

temperature = 33
if temperature > 30:
    print("It's hot — drink water!")

Three things to notice:

• The line ends with a colon : — Python's way of saying "a block is coming".
• The next line is indented by 4 spaces. That tells Python "this line belongs inside the if".
• If the condition is false, the indented line is simply skipped.

Part 4 · else — the "otherwise" path

Add an else branch for what should happen when the condition is false.

temperature = 24
if temperature > 30:
    print("It's hot — drink water!")
else:
    print("Nice weather today.")

Exactly one of the two branches runs — never both.

Part 5 · elif — many choices in a row

What if you have three or more paths? Chain them with elif (short for "else if").

score = 72
if score >= 80:
    print("Distinction!")
elif score >= 60:
    print("Pass.")
else:
    print("Try again next time.")

Python checks each line top-to-bottom. The first condition that is true wins — every later branch is skipped.

Part 6 · Indentation matters

Python uses indentation, not curly braces, to tell which lines belong together. Use 4 spaces at the start of every line that sits inside an if, elif or else.

The mamak shop on Jalan Bukit Bintang is running a school-holiday promo. Children pay half. Teenagers get a quarter off. Adults pay the full price. We'll build a tiny program that prints the right total. Save this as mamak_discount.py.

Code

# mamak_discount.py — work out the price after age discount

# 1. Ask the customer
name = input("What is your name? ")
age  = int(input("How old are you? "))

# 2. Full price for one nasi lemak + teh tarik
full_price = 8.00

# 3. Pick a discount based on age
if age < 12:
    discount = 0.50         # children: 50% off
elif age <= 17:
    discount = 0.25         # teens: 25% off
else:
    discount = 0.00         # adults: no discount

# 4. Calculate the final price
final_price = full_price * (1 - discount)

# 5. Print the receipt
print()
print("Hi", name + "!")
print("Full price:    RM", full_price)
print("Your discount:", int(discount * 100), "%")
print("You pay:       RM", final_price)

Two sample runs (lines you type are bold):

Output · child

What is your name? <strong>Priya</strong>
How old are you? <strong>9</strong>

Hi Priya!
Full price:    RM 8.0
Your discount: 50 %
You pay:       RM 4.0

Output · adult

What is your name? <strong>Wei Jie</strong>
How old are you? <strong>34</strong>

Hi Wei Jie!
Full price:    RM 8.0
Your discount: 0 %
You pay:       RM 8.0

What changed from PY-L1-07?

In PY-L1-07 every customer paid the same. Today our program chooses a discount based on the age the user types — same input shape, much smarter output.

Type each task into your editor. Run it. Try at least two different inputs before moving on.

Our programs can now choose. We compared values with ==, !=, < and friends, and used if / elif / else to pick a path. Indentation tells Python which lines belong inside each branch.