Python Lists

List

Lists are used to store multiple items in a single variable.

Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.

Lists are created using square brackets:

List Items

List items are ordered, changeable, and allow duplicate values.

List items are indexed, the first item has index [0], the second item has index [1] etc.

Ordered

When we say that lists are ordered, it means that the items have a defined order, and that order will not change.

If you add new items to a list, the new items will be placed at the end of the list.

Changeable

The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.

Allow Duplicates

Since lists are indexed, lists can have items with the same value:

List Length

To determine how many items a list has, use the len() function:

List Items - Data Types

List items can be of any data type:

A list can contain different data types:

type()

From Python's perspective, lists are defined as objects with the data type 'list':

The list() Constructor

It is also possible to use the list() constructor when creating a new list.

Python Collections (Arrays)

There are four collection data types in the Python programming language:

• **List** is a collection which is ordered and changeable. Allows duplicate members.
• **Tuple** is a collection which is ordered and unchangeable. Allows duplicate members.
• **Set** is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
• **Dictionary** is a collection which is ordered** and changeable. No duplicate members.

When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.