if, elif and else

The if statement

if runs some code only when a condition is True:

temperature = 35
if temperature > 30:
    print("It's hot! Drink water.")
print("Have a nice day.")

Output

It's hot! Drink water.
Have a nice day.

Two important details:

• The line with if ends with a colon :.
• The code that belongs to the if is indented (pushed right by 4 spaces). This indented group is called a block.

The last line isn't indented, so it always runs.

Think of it like this: Indentation is like the steps under a heading in a to-do list. Everything indented under “If it rains” only happens when it rains.

if ... else

else gives a plan B: the code to run when the condition is False.

age = 15
if age >= 18:
    print("You can vote.")
else:
    print("You can't vote yet.")

Output

You can't vote yet.

elif: more than two choices

elif means “else if”. Python checks each condition from top to bottom and runs the first one that is True. The rest are skipped.

marks = 72
if marks >= 90:
    print("Grade A")
elif marks >= 75:
    print("Grade B")
elif marks >= 50:
    print("Grade C")
else:
    print("Keep practising!")

Output

Grade C

72 isn't ≥ 90 or ≥ 75, but it is ≥ 50, so we get Grade C.

With input

number = int(input("Enter a number: "))
if number % 2 == 0:
    print(number, "is even")
else:
    print(number, "is odd")

Output (when you type 7)

Enter a number: 7
7 is odd

Common mistake: Forgetting the colon or the indentation. Both cause an error. Most editors indent automatically after you type a colon and press Enter.

Remember: Only one block runs in an if / elif / else chain – the first one whose condition is True.