Project: Shopping cart

Real programs mix collections: a dict for the price lookup and a list for what's in the cart.

See it run

prices = {"tea": 2, "jam": 3}
bag = ["jam", "tea"]
first = bag[0]
cost = prices[first]
print(first, cost)

The two collections work as a team: the list gives you names, the dict turns each name into a price.

Practice project: shopping cart

Exercise 1

Use cart and prices in the editor below. Make total the price of everything in cart (each name looked up in prices) using a loop or sum. Then print it as Total: $4.45.

Exercise 2

Use cart and prices in the editor below: this cart is a dict of name to quantity. For each item print a receipt line like apple x3 = $1.50 (money with 2 decimals), keep a running total, and finish with Total: $3.90.

Exercise 3

Use cart and prices in the editor below. Some cart items aren't in prices (out of stock).

Skip unknown items and collect their names in a list missing.
total = the cost of the known items.
If total is over 4, take 10% off to get final; otherwise final equals total.
Print Missing: cheese (names joined by ", ") and then Total: $4.23.

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Practice

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Visualizer Watch your code run line by line

Run your code, then choose Play to follow its execution.

Memory · names → values

Variables appear here as Python creates them.

Output & plots