Gallery

Intro to Python

Explore

Gallery

Intro to Python

Learn Python

Lists, Sets, and Dictionaries

This section covers:

Lists

Sets

Dictionaries

⁠

In this section, you’ll learn more about three types of data structures. You can think of them as ways to organize and store data.

Lists

Lists are used to store sequences of values. They are useful if you want to keep track of the order of the values. The values in the list are called elements or items.

Here are some examples of lists. Notice how lists can store any number of items of any type. Lists can also be empty.

⁠

View code on Python Tutor⁠

⁠

Accessing list elements

You can access elements in a list by using index notation. The first element is at index 0. For example, running print(cheeses[1]) will print Edam.

Adding elements

You can add elements to a list by calling the append function.

⁠

View code on Python Tutor⁠

⁠

Removing elements

You can also remove elements from a list in a couple ways. If you know the index of the element, you can use pop.

⁠

View code on Python Tutor⁠

⁠

If you know the element you want to remove, but you don’t know its index, you can use remove. This function does not return anything.

⁠

View code on Python Tutor⁠

⁠

Length of a list

Here is how you get the length of a list:

⁠

View code on Python Tutor⁠

⁠

Checking list membership

You can use the in keyword to check if an element is contained in a list. The expression will return True if the list contains the element and False otherwise.

Sets

Sets are like lists, but they do not store duplicate entries, and they are unordered (i.e. there is no “first” element in a set).

Here is how you can create a set in Python:

⁠

View code on Python Tutor⁠

⁠

Adding elements

You can add elements to a set by calling the add function.

⁠

View code on Python Tutor⁠

⁠

If you try to add an element that is already in the set, Python will ignore the add.

⁠

View code on Python Tutor⁠

⁠

Removing elements

You can remove elements in a set by calling the remove function.

⁠

View code on Python Tutor⁠

⁠

Checking set membership

You can use the in keyword to check if an element is contained in a set. The expression will return True if the set contains the element and False otherwise.

Dictionaries

Dictionaries are useful when you want to store values associated with a particular “key”. For example, if you want to keep track of your friend’s phone numbers, you can use a dictionary.

You can also add or update each key-value pair individually.

⁠

View code on Python Tutor⁠

⁠