Altcademy - a Forbes magazine logo Best Coding Bootcamp 2023

What is an array in Python

Understanding Arrays in Python

When you begin your journey as a programmer, you'll quickly come across the need to store multiple items in a single variable. This is where the concept of an array comes into play. Think of an array as a shelf where you can neatly line up your books, with each book representing a piece of data. In Python, arrays can be thought of in a similar way, but it's important to note that Python doesn't have built-in support for arrays as some other languages do. Instead, it offers a more flexible type called a list that functions similarly to an array in other programming languages.

The Basics of Python Lists

In Python, a list is a collection of items that can be changed, meaning you can add, remove, or modify items after the list has been created. You can imagine a list as a row of boxes, each containing an item, and you have the freedom to put something in a box, replace it with something else, or even remove it entirely.

Here's how you can create a list in Python:

my_first_list = [1, 2, 3, 4, 5]

When you run this code, you'll see the output [1, 2, 3, 4, 5]. This is a simple list of integers (whole numbers).

Accessing Elements in a List

To access an element in a list, you use its index, which is the position of the item in the list. It's important to remember that Python is zero-indexed, which means the first item is at index 0, the second at index 1, and so on.

Here's how you can access the first item of the list:

first_item = my_first_list[0]

The output will be 1 because that's the item at index 0.

Modifying Lists

Lists are mutable, which is just a fancy way of saying that they can be changed after creation. You can add items, remove items, or change the value of an item.

Adding Items

To add an item to the end of a list, you use the .append() method:


Now my_first_list will output [1, 2, 3, 4, 5, 6].

Removing Items

To remove an item, you can use the .remove() method:


The list will go back to [1, 2, 3, 4, 5].

Changing an Item

You can change an item by simply assigning a new value to it at a specific index:

my_first_list[0] = 100

Now the first item is 100, so the list prints [100, 2, 3, 4, 5].

Iterating Over a List

Often, you'll want to go through each item in a list and perform an action. This is called iteration. In Python, the most common way to iterate over a list is with a for loop.

for item in my_first_list:

This will print each item in my_first_list on a new line.

When to Use Lists

Lists are incredibly versatile and can be used in a wide range of situations. Whenever you have a collection of items that belong together, a list is often a good choice. Whether it's a list of names, numbers, or even other lists (yes, you can have lists within lists!), they provide a way to keep your data organized and accessible.

Limitations and Alternatives

While lists are great for many situations, they aren't always the most efficient choice, especially when dealing with large amounts of data or when you need to perform lots of numerical computations. In these cases, you might want to look into using arrays provided by the numpy library, which are more memory-efficient and offer faster performance for numerical operations.

Here's a quick example of how you can use a numpy array:

import numpy as np

my_numpy_array = np.array([1, 2, 3, 4, 5])

numpy arrays have similar functionality to lists but are optimized for numerical computations.

Practical Examples

Let's see some practical examples of how lists can be used in Python programs.

Example 1: A List of Square Numbers

squares = [number**2 for number in range(10)]

This code snippet creates a list of the squares of numbers from 0 to 9.

Example 2: A List of Usernames

usernames = ["user1", "user2", "user3"]

A simple list to store usernames.

Example 3: A To-Do List

todo_list = ["Buy groceries", "Call mom", "Water the plants"]

A to-do list created using a Python list.

Conclusion: Embrace the Flexibility of Lists

As you embark on your programming journey, mastering lists in Python will be an invaluable skill. They are the Swiss Army knife in your toolkit, ready to adapt to whatever data you need to store and manipulate. By understanding and utilizing lists, you'll be able to handle a wide array of programming tasks with ease.

Remember, a list is like a friend that helps you keep your data in check—flexible, reliable, and always there when you need to organize your thoughts (or in this case, your code). Whether you're making a simple to-do app or preparing data for complex analysis, lists are your stepping stone towards becoming an adept Python programmer. So go ahead, create some lists, and start coding your way to success!