Making Decisions with if/else

Programs get interesting when they can make choices. The if statement lets your code run only when a condition is true.

The shape of an if

age = 20
if age >= 18:
    print("You are an adult.")

Read it as plain English: "if age is greater than or equal to 18, then show that message." Two things to notice:

• The line ends with a colon :
• The line below is indented (pushed in with spaces). That indentation is how Python knows which code belongs to the if. It's not decoration — it's required.

Adding else

else covers the "otherwise" case — what to do when the condition is not true:

age = 15
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

Comparing values

These are the comparison operators you'll use:

• == equal to (yes, two equals signs — one is for storing)
• != not equal to
• > greater than, < less than
• >= greater than or equal, <= less than or equal

Checking more cases with elif

elif (short for "else if") lets you check extra conditions in order:

score = 75
if score >= 90:
    print("Grade A")
elif score >= 70:
    print("Grade B")
else:
    print("Keep going!")

Your turn

Change the value of score and see which message prints.