List in Python

Good morning! Today, I’m going to share what I’ve been learning about lists in Python.

I’ll explain what a list is, how to add items to it, how to modify an item, and how to delete an item from a list.

What is a List in Python?

A list in Python is a data type that allows you to store multiple items in a single variable. For example, we can create a variable that holds just one name, but a list lets us store multiple names or numbers together.

Think of a list as a container that can hold multiple items of different types, such as numbers, strings, or Boolean values.

How to Create a List

To create a list in Python, we use square brackets []. Here’s an example:

names = ["Peter", "Luke", "Avery"]

Lists with Different Data Types

You can create a list that holds only numbers:

numbers = [1, 2, 5, 10, 29]

Or, you can mix different data types (numbers, strings, Booleans) in a single list:

everything_list = [1, "Luke", True]

Understanding List Indexing

Lists in Python are zero-indexed, meaning that each item has a position (index), and counting starts at 0 instead of 1.

For example, in this list:

names = ["Peter", "John", "Luke"]

• "Peter" is at index 0
• "John" is at index 1
• "Luke" is at index 2

Accessing an Item in a List

Knowing the index, we can access an item in the list:

print(names[0])  # First item (Peter)
print(names[1])  # Second item (John)

Accessing the Last Item in a List

If a list has 6 items, the last index will be 5 (total items - 1):

names[5]  # Access the last item if there are 6 items

Python also provides an easier way to access the last item using negative indexing:

print(names[-1])  # Prints the last item

Adding Items to a List

In Python, we can use the append() function to add an item to the end of a list:

names.append("Mary")
numbers.append(40)

Inserting an Item at a Specific Position

Another way to add an item to a list is by using the insert() function.

The insert() function allows us to add an item at a specific position in the list.

For example, if I want to add "Paula" to the second position (index 1), I will do:

names.insert(1, "Paula")

This will insert "Paula" at the second position, pushing the existing items to the right.

Updating an Item in a List

To modify an item, we use the list name, specify the index we want to edit, and assign a new value:

names[0] = "Chloe"

Now, the first item (index 0) is updated from "Peter" to "Chloe".

Deleting an Item from a List

If you want to delete an item from a list using its index, you can use the del keyword:

del names[1]  # Deletes the item at index 1

Removing an Item by Value

If you want to remove an item based on its value rather than its index, use the remove() function:

names.remove("Chloe")  # Removes "Chloe" from the list

Sorting a List

If you want to sort the items in a list in ascending order, you can use the sort() function:

names.sort()

Important Note:

When you use sort(), the list is modified in place, meaning you won’t have access to the original, unsorted list unless you make a copy beforehand.

If you want to sort a list without modifying the original, use sorted():

sorted_names = sorted(names)  # Returns a new sorted list

Looping Through a List

You can iterate through a list and print each item using a for loop:

for item in names:
    print(item)

This will print each item in the list one by one.

Creating a List of Numbers Using range()

One way to create a list of numbers is by using the range() function.

For example:

numbers = list(range(0, 10))  # Creates a list from 0 to 9
print(numbers)  # Output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

You can also iterate through a list of numbers using range():

for num in range(1, 6):  # Loops from 1 to 5
    print(num)

Copying a List

You can copy a list from another list by assigning the old list to a new variable:

new_list = numbers

⚠️ Warning:

If you copy a list this way, new_list will still be linked to numbers, meaning that changes in one list will affect the other.

Creating an Independent Copy

To create a separate copy, use slicing ([:]):

new_list = numbers[:]  # Creates a new independent copy