Looping through a list

You are going to use iteration and lists to create a program which will create and display a shopping list for you. You will create this program in two parts: one to displaying the shopping list, and another to create it. Your challenge will be to combine these two programs together.

We’ll start with the code to display the shopping items. The first step is to create a program which will loop through all the items in a list and print them to the screen.

• Create a new program and save it as display_shopping.

Note: If you are unsure how to do this, take a look at the “If it’s this, then do that” step from Week 2.

• Create a list variable for your shopping and fill it with some items.

shopping = ["bread", "cheese", "apple", "tomato", "biscuits"]

To loop through each of the items in the list, you will use a for loop. for loops exist in most programming languages, and their purpose is to allow code to be run a set number of times – in our case, equal to the number of things in our shopping list.

The syntax of a for loop in Python looks like this:

for element in list:
 print("do this")

• Use a for loop to print out each of the items in your shopping list.

for item in shopping:
 print(item)

Note: The print statement is indented under the for loop. Indentation in a for loop works exactly the same as in an if statement; whatever code is indented under the for is run as part of that loop.

• Run your program.

Let’s break this down and consider what steps the computer takes to carry out this program.

• First it creates the list called shopping.

shopping = ["bread", "cheese", "apple", "tomato", "biscuits"]

• The for loop is entered. The first element in the shopping list, "bread", is put into the variable item.

for item in shopping:

• print is used to display what is in the variable item.

 print(item)

• item holds the value “bread”, so “bread” is printed.

bread

• The for then runs again and the second element in the shopping list, "cheese" is put into the variable item.

for item in shopping:

• print is used to display what is in the the variable item.

 print(item)

• This time, item holds the value “cheese”, so “cheese” is printed.

cheese

• The for loop runs again and the third element, "apple", is put into the variable item.

for item in shopping:

• This continues until there are no more items in the list. Each item has been printed in turn, and then the for loop stops.