2.1 Conditionals

Conditionals let your program make decisions: run one block of code when something is true, and a different block when it’s false.

if

Use if and a condition. The code that runs when the condition is true is indented (usually 4 spaces):

score = 50
if score >= 50:
    print("You passed!")

If score were 30, nothing would print. Only when score >= 50 is True does the indented code run.

Indentation matters

In Python, indentation shows which lines belong to the if. Everything that’s indented under if runs only when the condition is True.

if score > 0:
    print("Score is positive")
    print("Well done")
print("This always runs")  # not indented, so not part of the if

else

Use else to run code when the condition is not true:

age = 12
if age >= 13:
    print("You can join")
else:
    print("Come back when you're 13")

elif (else if)

Use elif to check another condition when the first one was false:

score = 75
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
else:
    print("Keep practising")

Only one of these blocks runs: the first condition that is True.

Mini project: Secret number (one guess)

1. Choose a secret number and store it in a variable.
2. Use input() to get the user’s guess (convert to int).
3. Use if, elif and else to print “Too high!”, “Too low!” or “Correct!”.
4. (In the next lesson we’ll add a loop so they can keep guessing.)

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Navigation

• Previous: 1.3 Operators
• Next: 2.2 Loops
• All lessons: Lesson list on the homepage

Tasks

• Unit 2 tasks - lots of practice with if, elif, and else (e.g. menus, grades, tickets; loops come in too on many pages)

Tutorial

• Tutorial 2.1 - guided project for this unit