Combining and Nesting Conditions

Why this matters

Real rules are rarely a single yes/no question: free for children, but only on weekdays; members get a discount unless the item is already on sale. You build rules like these by combining conditions and nesting if statements.

The idea

You already know and, or and not from the Booleans lesson. They work directly inside if:

age = 20
has_ticket = True

if age >= 18 and has_ticket:
    print("Come in")

or is true if either side is:

day = "sat"
if day == "sat" or day == "sun":
    print("Weekend")

A shorter way to check against several options is the in operator:

if day in ("sat", "sun"):
    print("Weekend")

You can also put an if inside another if. The inner one is indented further and only runs if the outer condition was true:

if age >= 18:
    if has_ticket:
        print("Come in")
    else:
        print("Buy a ticket first")
else:
    print("Too young")

Nesting is great when a second question only makes sense after the first. When you can express the same thing with and, that is usually shorter and easier to read.

Another useful trick: a variable can be changed in one if and used in the next:

price = 10
if day in ("sat", "sun"):
    price = price + 2
print(price)

Try it

Rewrite the nested example above using and instead of nesting. Try different values of age and has_ticket and check you get the same results.

Your turn

A cinema sets the ticket price from the customer’s age:

Age	Base price
under 5	$0 (free)
5 to 12	$8
13 to 64	$15
65 or over	$10

On weekends (sat or sun) every ticket that is not free costs $2 more. The starter reads the age and the day (always in lowercase, like mon or sat). Print the price in the form Ticket: $17.

Recap

• Combine conditions in one if with and, or and not.
• x in (a, b, c) checks several options at once.
• Nest an if inside another when the second question depends on the first.

Common mistakes

• if day == "sat" or "sun": this does not do what it looks like. Write day == "sat" or day == "sun", or use in.
• Wrong indentation in nested blocks: each level needs four more spaces.
• Applying the surcharge to free tickets. Check the price before adding.