What are Lists?

Lists are Python's most versatile data container. They let you store multiple items together inside square brackets [] in a specific order.

Think of a list like:

• A shopping list (milk, eggs, bread)
• A to-do list (tasks in order)
• A playlist (songs in sequence)

Creating Lists

You create a list by placing items separated by commas inside square brackets []:

# An empty list
shopping_cart = []

# A list of text strings
fruits = ["apple", "banana", "orange"]

# A list of numbers
scores = [95, 88, 72, 100]

# You can even mix different data types in the same list!
mixed_item = ["Alice", 25, True, 3.14]

Accessing Items by Index

Just like strings, every item in a list has a numbered position starting from 0:

fruits = ["apple", "banana", "orange"]

# Grab the first item
print(fruits[0])   # Output: apple

# Grab the second item
print(fruits[1])   # Output: banana

# Grab the last item using negative indexing
print(fruits[-1])  # Output: orange

Changing Items inside a List (Mutability)

Unlike strings, lists can be changed after you create them! You can replace any item by assigning a new value to its index position:

fruits = ["apple", "banana", "orange"]

# Replace "apple" with "mango"
fruits[0] = "mango"
print(fruits)  # Output: ['mango', 'banana', 'orange']

Slicing a List

You can extract a smaller sub-list using a colon [start:stop]:

numbers = [10, 20, 30, 40, 50]

# Grab items from index 1 up to index 3
print(numbers[1:4])  # Output: [20, 30, 40]

Checking if an Item Exists (in)

You can easily check if a specific item is inside your list using the in keyword:

fruits = ["apple", "banana", "orange"]

if "banana" in fruits:
    print("Yes, banana is in the shopping list!")

Common Beginner Mistakes

Index out of range

# Wrong - list only has 3 items (indices 0, 1, 2)
fruits = ["apple", "banana", "orange"]
print(fruits[3])  # IndexError: list index out of range

# Right - check how many items are in the list first using len()
if len(fruits) > 3:
    print(fruits[3])
else:
    print(fruits[-1])  # Print the last item instead

What's Next?

Now let's explore all the essential list methods for adding, removing, counting, searching, and sorting items.

List Methods & Operations

Master append(), insert(), remove(), pop(), sort(), count(), and copy()