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🐍 Python Basics Topic 17 / 100

⏱ 9 min read

if Statements

Making your program make decisions — the most important concept in all of programming, explained simply with everyday examples.

"An if statement is just your program saying: 'If this is true — do this. Otherwise — do something else.' You already think this way. Python just lets you write it down."

— ShurAI

You Already Think in if-statements

Before you ever touch code, you make hundreds of if-decisions every day. Your brain runs them automatically:

🌧️

If it is raining
→ take an umbrella
else
→ leave it at home

🔋

If battery < 20%
→ plug in charger
else
→ keep using phone

🎫

If age ≥ 18
→ allowed in
else
→ entry denied

Python's if statement lets you write exactly this kind of logic in code.

The Basic Shape of an if Statement

Here is the structure. Three things matter: the keyword if, a condition that is either true or false, and a colon : at the end. The indented code below runs only if the condition is True.

            if
             
            condition
            :
          

            indented code runs if condition is True
          
↑
keyword
↑
any True/False expression
↑
required colon!

Example 1 — Is it Hot Outside?

The simplest possible if statement. If the temperature is over 35, print a message. Otherwise, do nothing:

python

temperature = 38

if temperature > 35:
    print("It's too hot! Stay indoors.")
    print("Drink lots of water.")

print("Have a nice day!")

output

It's too hot! Stay indoors.
Drink lots of water.
Have a nice day!

Now change temperature = 28 and run it again. The two indented lines are skipped — but "Have a nice day!" always prints because it is not indented under the if block.

Indentation — The Most Important Rule

In Python, indentation is not just style — it is the rule. The indented lines belong to the if block and only run when the condition is True. Lines that go back to the left edge always run.

if score >= 60:
← always evaluated
print("Pass!")
↑ only runs when score ≥ 60
print("Well done")
↑ only runs when score ≥ 60
print("Done")
↑ always runs — not in the if block

Use 4 spaces for indentation

Python standard is 4 spaces per indent level. Never mix tabs and spaces — Python will give you an IndentationError. Most code editors handle this automatically when you press Tab.

if...else — One or the Other

Add an else block to handle the case when the condition is False. Exactly one of the two blocks will always run:

python

age = 16

if age >= 18:
    print("You can vote!")
else:
    print("You are too young to vote.")
    print(f"Wait {18 - age} more year(s).")

output

You are too young to vote.
Wait 2 more year(s).

More Everyday Examples

python — password check

password = input("Enter password: ")

if password == "shurai123":
    print("✅ Access granted! Welcome.")
else:
    print("❌ Wrong password. Try again.")

python — even or odd number

number = int(input("Enter a number: "))

if number % 2 == 0:
    print(f"{number} is an EVEN number")
else:
    print(f"{number} is an ODD number")

python — shopping discount

total = float(input("Cart total (Rs.): "))

if total >= 1000:
    discount = total * 0.10   # 10% off
    print(f"🎉 You get Rs.{discount:.0f} off!")
    print(f"You pay: Rs.{total - discount:.0f}")
else:
    needed = 1000 - total
    print(f"Add Rs.{needed:.0f} more to get 10% off!")

if...elif...else — Multiple Choices

elif means "else if" — it adds more conditions to check. Python tests them top to bottom and runs the first one that is True. Think of it like a flowchart:

python — exam grades

marks = int(input("Your marks (0-100): "))

if marks >= 90:
    print("Grade A+ — Outstanding! 🏆")
elif marks >= 80:
    print("Grade A — Excellent! 🌟")
elif marks >= 70:
    print("Grade B — Good work! 👍")
elif marks >= 60:
    print("Grade C — Satisfactory")
elif marks >= 35:
    print("Grade D — Just passed")
else:
    print("Grade F — Failed. Keep trying! 💪")

🧠 How Python reads this — one step at a time:

Is marks >= 90?  → No   keep going
Is marks >= 80?  → No   keep going
Is marks >= 70?  → Yes!   run this block, stop here
Is marks >= 60?  → skipped
Is marks >= 35?  → skipped
else              → skipped

Once one condition matches, Python runs that block and jumps past all the rest.

Common Mistakes to Avoid

python — mistake 1: missing colon

# ❌ SyntaxError — colon is missing
if age >= 18
    print("adult")

# ✅ Correct
if age >= 18:
    print("adult")

python — mistake 2: = instead of ==

# ❌ SyntaxError — = is assignment, not comparison
if name = "Riya":
    print("hello")

# ✅ Correct — use == to compare
if name == "Riya":
    print("hello")

python — mistake 3: wrong indentation

# ❌ IndentationError — no indent inside if
if score >= 50:
print("pass")

# ✅ Correct — 4 spaces inside the if block
if score >= 50:
    print("pass")

Real Example — Movie Ticket Pricing

A ticket booking system that uses age and day of week to calculate the price:

python

print("=== 🎬 Movie Ticket Booking ===")
age = int(input("Your age       : "))
day = input("Day (Mon-Sun)  : ").lower()

# Base price by age group
if age < 5:
    price = 0
    category = "Child (free)"
elif age < 12:
    price = 80
    category = "Child"
elif age < 60:
    price = 200
    category = "Adult"
else:
    price = 120
    category = "Senior"

# Tuesday discount — cheapest day
if day == "tuesday":
    price = price * 0.5   # 50% off on Tuesdays

print()
print(f"Category  : {category}")
print(f"Day       : {day.title()}")
print(f"Ticket    : Rs.{price:.0f}")

terminal — example run

=== 🎬 Movie Ticket Booking ===
Your age       : 28
Day (Mon-Sun)  : Tuesday

Category  : Adult
Day       : Tuesday
Ticket    : Rs.100

Quick Summary of if Statement Forms

You have three choices: just if (runs or skips), if...else (runs one of two options), and if...elif...else (runs one of many options). You will use all three constantly — knowing which one to reach for is the skill.

"Every useful program has if statements. They are not just a feature — they are the heartbeat of all logic."

— ShurAI

🧠 Quiz — Question 1

What happens if you forget the colon : at the end of an if statement?

🧠 Quiz — Question 2

What is the standard number of spaces used for indentation inside an if block?

🧠 Quiz — Question 3

score = 75. Which message does this print?
if score >= 90: print("A") elif score >= 70: print("B") elif score >= 60: print("C") else: print("F")

🧠 Quiz — Question 4

In an if...elif...else chain, how many blocks will actually run?