Introduction to Lists

Todo, agendas, names, phone numbers - all the information you need in one place!

What is a list?

A list is a collection of data in an ordered list.

Examples of Lists

Names of people in your address book
Important telephone numbers
To-do list

Declaring a List

Declaring a list is simple - just enclose your list in brackets and separate each element with comma.


                        shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        print(shows)


                        ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']

Elements in a List

Lists store data in a sequential manner, every element has a number which tells us its position in a list.

This number is called an index (singular) or indices (plural).
Indices in computer science generally start from the number 0.
You can start from the end of the list and go backwards by using the index -1 and decreasing the index.

Accessing Elements in a List

Python gives us a simple way to access any element in a list given the index


                        shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        print(shows)
                        print(shows[1])
                        print(shows[1].upper())
                        print(shows[-1].upper())


                        > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        > Arrested Development
                        > ARRESTED DEVELOPMENT
                        > BREAKING BAD

Line 4 shows that you can also call methods such as .upper() after accessing the element.

Using Values Stored in a List

You can use an element stored in a list by accessing its index and using f-strings .


                        shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        print(f"My favorite show is {shows[1]}, I heard your favorite show is {shows[3]}.")


                        >  My favorite show is Arrested Development, I heard your favorite show is Breaking Bad.

Modifying Values in a List

Modifying a value from a list is very easy - just supply the index and assign it a new value.


                        shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        print(shows)
                        # Change the third element of the list.
                        shows[2] = 'Clifford'
                        print(shows)


                        > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                        > ['DBZ', 'Arrested Development', 'Clifford', 'Breaking Bad']

Adding New Elements to the end of a List

Elements can be added to the end of a list by using the append() method on a list.

This is great because you do not need to know the length of the list to add a new element at the end.


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Add an element to the end of the list
                            shows.append('Curious George')
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad', 'Curious George']

Adding Elements to a Specific Index

You can add an element to a specific position in the list by using the insert() method.


              list.insert(index,value)

This causes your element to be added at the specified index and it shifts all other elements to the right one index.


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Add an element to index 1
                            shows.insert(1,'NCIS')
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > ['DBZ', 'NCIS', 'Arrested Development', 'The Simpsons', 'Breaking Bad']

Removing Elements from a List

The `del` command

You can remove any element from a list using the del command.


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Delete the 3rd element
                            del shows[2]
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > ['DBZ', 'Arrested Development', 'Breaking Bad']

The `pop()` method

If you would like to have delete and element and have access to its value you can use the pop() method.

If you call the method without an argument its default behavior is to pop the last element in a list.


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Pop the last element and print it to a string.
                            print(f'My favorite show is {shows.pop()}.')
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > My favorite show is Breaking Bad.
                            ['DBZ', 'Arrested Development', 'The Simpsons']

Popping a specific element

Supplying an index number to the pop command allows you to choose which element you pop.


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Pop the last element and print it to a string.
                            print(f'My favorite show is {shows.pop(1)}.')
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > My favorite show is Arrested Development.
                            ['DBZ', 'The Simpsons', 'Breaking Bad']

Removing Elements by Value

Instead of removing and element by its index, you can instead search for a specific value, x, and remove it using the remove(x) method


                            shows = ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            print(shows)
                            # Remove the first occurence of 'The Simpsons'
                            shows.remove('The Simpsons')
                            print(shows)


                            > ['DBZ', 'Arrested Development', 'The Simpsons', 'Breaking Bad']
                            > ['DBZ', 'Arrested Development', 'Breaking Bad']