The ‘investigate’ stage gives students some example code and asks them questions about it to check their understanding. I use the block model to plan my questions. Try it, it’s really useful.

A list is an example of a data structure. This is the name for a number of different programming techniques used to organise and manipulate data in programs.

So far to store data in the program we have used variables, which hold one piece of data and use an identifier (variable name) to represent it in the code.

Lists work in the same way as variables, but they can store multiple items of data using one identifier rather than just one.

Lists are created in Python like this:

# List of strings
countries = ["UK", "USA", "Chad", "Australia", "Thailand", "Canada"]

# List of integers
prime_numbers = [1,3,5,7,11,13]

To identify individual items in a list, the data is indexed (given a number). Indexing starts at 0, meaning that the first item in a list will be number 0, the second number 1 and so on.

We can also print an individual item from a list or the entire list using the following syntax:

# This will print 'UK'
print(countries[0])

# This will print 'Canada'
print(countries[5])

# This will print the entire list
print(countries)

We can change items in lists by using the assignment operator (=) with the index of the item to be changed.

# Changes the first item in the 'countries' list to 'France'
countries[0] = "France"

Here are some other useful methods that can be used with lists

Python makes it really easy to check if an item is in a list. This is where we can start to combine what we’ve previously learned about selection with lists. The code for this is:

if "item" in list_name:
	# Run this code if condition is true

Make sure that you check for the following things:

• The list name is identical everywhere it is used (capitals matter)
• List index is surrounded by square brackets
• List indexing starts at zero – are you counting properly?