Making Decisions with if/elif/else

Conditional statements let your program make decisions. Python uses if, elif (else if), and else to execute different blocks of code depending on whether a condition is True or False.

score = 85

if score >= 90:
    print("Grade: A - Outstanding!")
elif score >= 80:
    print("Grade: B - Well done!")
elif score >= 70:
    print("Grade: C - Good effort")
elif score >= 50:
    print("Grade: D - Pass")
else:
    print("Grade: F - Needs improvement")

Output: Grade: B - Well done!
Python checks each condition from top to bottom and runs the first one that is True.

Comparison and Logical Operators

Comparison operators compare two values and return True or False. Logical operators combine multiple conditions.

Comparison Operators

== Equal to

!= Not equal to

> Greater than

< Less than

>= Greater or equal

<= Less or equal

Logical Operators

and Both must be True

or At least one True

not Reverses True/False

age = 16
has_permit = True

# Using logical operators
if age >= 16 and has_permit:
    print("You can drive with a supervisor")
elif age >= 16 and not has_permit:
    print("Get your learner's permit first")
else:
    print("You are not old enough to drive yet")

# Combining conditions
temp = 25
if temp > 30 or temp < 10:
    print("Extreme weather!")
else:
    print("Nice weather today")

Nested Conditions

You can place an if statement inside another if statement. This is called nesting. Be careful with indentation, as Python uses it to determine which code belongs to which block.

is_member = True
purchase_amount = 120

if is_member:
    if purchase_amount >= 100:
        discount = 20
        print(f"Member with ${purchase_amount} purchase: {discount}% off!")
    else:
        discount = 10
        print(f"Member discount: {discount}% off")
else:
    if purchase_amount >= 100:
        discount = 5
        print(f"Non-member bulk discount: {discount}% off")
    else:
        discount = 0
        print("No discount available")

Output: Member with $120 purchase: 20% off!

Key Vocabulary

Conditional

A statement that executes code only when a specified condition is True.

Boolean Expression

An expression that evaluates to either True or False.

Comparison Operator

Symbols like ==, !=, >, < that compare two values.

Logical Operator

Keywords and, or, not that combine boolean conditions.

Worked Examples

1

Check if a number is positive, negative, or zero

number = -7

if number > 0:
    print(f"{number} is positive")
elif number < 0:
    print(f"{number} is negative")
else:
    print("The number is zero")

Step 1: First check if number > 0. Since -7 is not > 0, this is False.

Step 2: Then check elif number < 0. Since -7 < 0, this is True.

Output: -7 is negative

2

Validate a password with multiple conditions

password = "Secure123"

has_upper = any(c.isupper() for c in password)
has_digit = any(c.isdigit() for c in password)
long_enough = len(password) >= 8

if has_upper and has_digit and long_enough:
    print("Strong password!")
elif long_enough:
    print("Weak password: add uppercase and numbers")
else:
    print("Too short: must be at least 8 characters")

Step 1: We check three conditions: uppercase letters, digits, and length.

Step 2: The and operator ensures all three must be True. Output: Strong password!

3

Determine ticket price based on age and day

age = 16
day = "Tuesday"

if age < 5:
    price = 0
    category = "Free (under 5)"
elif age <= 17:
    price = 12
    category = "Child"
elif age >= 65:
    price = 15
    category = "Senior"
else:
    price = 25
    category = "Adult"

# Tuesday discount
if day == "Tuesday":
    price = price * 0.5
    print(f"{category} ticket on Tuesday: ${price:.2f} (half price!)")
else:
    print(f"{category} ticket: ${price:.2f}")

Step 1: Age 16 matches the elif age <= 17 condition, so price = $12.

Step 2: It is Tuesday, so the price is halved. Output: Child ticket on Tuesday: $6.00 (half price!)

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

What is the output of: if 10 > 5: print("Yes")?

No Yes True Error

Question 2

Which operator checks if two values are equal?

= != == ===

Question 3

What does True and False evaluate to?

True Error None False

Question 4

What does not True return?

False True None Error

Question 5

What keyword is used for "else if" in Python?

else if elif elseif otherwise

Python Conditionals