Receipts¶

In this chapter you will:¶

area	topic
🚀	sum up numbers from shopping bills
⚙	loop over a list
💡	use the `append` method of the `list` data type
🔀	transform a list into a new one
🐞	fix value errors

Exercise 1¶

To process larger amounts of data, we cannot invent a new variable name for every number. Instead, we can store multiple number in a list.

The program below sums up items on a list. Complete the code by inserting costs, for, item, total

costs = [8, 5, 20, 12, 1]
total = 0
___ item in ___:
    ___ += ___
print(total)

Exercise 2: List methods¶

Find out what each expression does to the list in the center.

Exercise 3: Add an extra item¶

You have an extra item you need to take into account:

costs = [8, 5, 20, 12, 1]
extra = 4

Use a list method from exercise 2 to add the extra item to the list. Then calculate the sum.

Exercise 4: Concatenate¶

Explain the difference between the following expressions:

[1, 2 + 3, 4]

[1, 2] + [3, 4]

["1", "2" + "3", "4"]

["1, 2" + "3, 4"]

"[1, 2" + "3, 4]"

Exercise 5: Puzzle¶

Use the expressions to modify the list as indicated. Use each expression once.

Exercise 6: List transformation¶

Sometimes it is useful to create a new list from an existing one. This is called transforming a list. Order the lines in the following program:

print(total)
costs = ["8", "5", "20", "12", "1"]
numbers.append(int(item))
for item in costs:
total = sum(numbers)
numbers = []

Exercise 7: Receipt assistant¶

Write a program that sums up shopping bills. The user enters amounts, one number at a time. If they enter nothing (an empty string), the program calculates the total value of the items entered.

The output of the program could look like this:

Please enter the costs on your bills, one number at a time:
13
8
5
21

The total cost of your bills is 47

Hint

You will need a while loop for entering the numbers.

Reflection Questions¶

How can you create a list?
How can you add an item to a list?
How can you run a for loop over a list?