Conditionals

Conditionals let your code make decisions based on whether something is true or false.

The if Statement

age = 18
if age >= 18:
    print("You can vote!")

Note: the indented code only runs when the condition is True.

if / else

temperature = 35
if temperature > 90:
    print("It's hot!")
else:
    print("It's not too bad.")

if / elif / else

Use elif (short for "else if") to check multiple conditions:

grade = 85
if grade >= 90:
    print("A")
elif grade >= 80:
    print("B")
elif grade >= 70:
    print("C")
else:
    print("Keep trying!")

Tip: Python checks conditions top to bottom and stops at the first match.

Comparison Operators

OperatorMeaning
==equal to
!=not equal to
<less than
>greater than
<=less than or equal to
>=greater than or equal to
 
name = "Alex"
if name == "Alex":
    print("Hey Alex!")

Logical Operators

Combine conditions with and, or, and not:

age = 16
has_permit = True

if age >= 16 and has_permit:
    print("You can drive!")

if age < 13 or age > 65:
    print("Discount available!")

if not has_permit:
    print("Get a permit first.")

Nested Conditionals

You can put conditionals inside other conditionals:

is_member = True
age = 15

if is_member:
    if age < 18:
        print("Junior member discount!")
    else:
        print("Member discount!")
else:
    print("Sign up for discounts!")

Common Mistakes

Using = instead of ==

# Wrong - this assigns, doesn't compare
if score = 100:

# Right - this compares
if score == 100:

Forgetting the colon

# Wrong
if age > 18
    print("Adult")

# Right
if age > 18:
    print("Adult")

Incorrect indentation

# Wrong - print is not indented
if age > 18:
print("Adult")

# Right
if age > 18:
    print("Adult")