Mastering Lists in Python

• Computing
• Lower Secondary (Key Stage 3)

Mastering Lists in Python

Unit 4 Programming

Said Ahghari

Learning Objective

By the end of the lesson, you will be able to understand how to declare, access, iterate through, and modify lists in Python.

Data Types

Python supports various data types such as integers, floats, strings, and Boolean.

Data Types for Variables

In Python, variables can hold different types of data, such as numbers, strings, boolean, and lists. Each data type has its own characteristics and usage.

Lists

In python one of the most used data structures is a list.

Lists are used to store data, one item after another.

For example:

• items you need to buy from a shopping list
• names of students in a class

A list is an example of a 1 Dimensional array.

What do you already know about using lists in Python?

List Data Type

Lists are a collection of items that can be manipulated and accessed individually. The list in Python is used to store multiple values in a single variable. It is denoted by square brackets ([]).

marks = [25, 65, 95, 33]    #a list of 4 numbers  

names = []                              #an empty list

Coding Activity: creating and outputting a list

In Python, create a list of 5 students.  Name the list myStudents. Output the list. 

Solution

myStudents = ["Said", "John", "Iman", "Nour", "Jane"]

print(myStudents)

List items' position

Each list item is held in a position (index) in the list.

The list index starts from zero (0).

0	1	2	3	4
Said	John	Iman	Nour	Jane

Position (index)

List item

Accessing Items in a List

List items have a position that is called index.  Individual items in a list are accessed using their index. Indexing starts at 0, and negative indexing can be used to access items from the end of the list.

students = ["Said", "John", "Ayesha", "Mohammed", "Jane"]

Index	0	1	2	3	4
Items	Said	John	Ayesha	Mohammed	Jane

Accessing Items in a List

Individual items in a list are accessed using their index. Indexing starts at 0, and negative indexing can be used to access items from the end of the list.

print (students [1]) 

print (students [-1])

What is the output?

Index	0	1	2	3	4
Items	Said	John	Ayesha	Mohammed	Jane

Finding the number of items in a list

To find the number of items in a list use the len() function.

myStudents = ["Said", "John", "Iman", "Nour", "Jane"]

print(len(myStudents))

Output:

5

Iterating Through a List

You can iterate through all the items in a list using a for loop. This allows you to perform operations on each item in the list.

students = ["Said", "John", "Ayesha", "Mohammed", "Jane"]

for x in students:

     print (x)

Adding Items to a List

New items can be added to a list using the append() method. This adds the new item to the end of the list.

students = ["Said", "John", "Ayesha", "Mohammed", "Jane"]

students.append("Ali")

students.append("Hassan")

print (students)

Replacing Items in a List

You can replace items in a list by directly assigning a new value to the specific index of the item.

students[0] = "Ali"

print (students)

Removing Items from a List

Items can be removed from a list using the remove() method or by using the del keyword followed by the index of the item to be deleted.

students.remove("Jane")

Practice and Questions

Now that you've learned about using lists in Python, it's time to practice and ask any questions you may have.

Write the code to print the last item in the following list:
students = ["Said", "John", "Ayesha", "Mohammed", "Jane"]

Write down 3 things you learned in this lesson.

Have students enter three things they learned in this lesson. With this they can indicate their own learning efficiency of this lesson.

Write down 2 things you want to know more about.

Here, students enter two things they would like to know more about. This not only increases involvement, but also gives them more ownership.

Ask 1 question about something you haven't quite understood yet.

The students indicate here (in question form) with which part of the material they still have difficulty. For the teacher, this not only provides insight into the extent to which the students understand/master the material, but also a good starting point for the next lesson.