Nested Lists | Python Tutorial

Nested Lists allow us to store lists inside another list. These are useful when we want to store structured or table-like data.

What are Nested Lists?

A nested list simply means a list that contains other lists as items.

# Nested List Example
students = [
    ["Harry", 20],
    ["Sarah", 22],
    ["Bruno", 21]
]
 
print(students)

Output:

[['Harry', 20], ['Sarah', 22], ['Bruno', 21]]

Each inner list represents a student's name and age.

Accessing Items in Nested Lists

To access elements inside nested lists, we use multiple indexes:

First index → selects the inner list
Second index → selects the item inside that inner list

# Accessing elements inside nested lists
students = [
    ["Harry", 20],
    ["Sarah", 22],
    ["Bruno", 21]
]
 
print(students[0][0])     # First student's name
print(students[1][1])     # Second student's age

Output:

Harry
22

Modifying Items in Nested Lists

We can change values inside nested lists using indexing.

# Modifying nested list items
students = [
    ["Harry", 20],
    ["Sarah", 22],
    ["Bruno", 21]
]
 
students[0][1] = 25       # Updating Harry's age
 
print(students)

Output:

[['Harry', 25], ['Sarah', 22], ['Bruno', 21]]

Iterating Through Nested Lists

1. Looping through each inner list

# Looping through nested lists
students = [
    ["Harry", 20],
    ["Sarah", 22],
    ["Bruno", 21]
]
 
for student in students:
    print(student)

Output:

['Harry', 20]
['Sarah', 22]
['Bruno', 21]

2. Looping through each value inside inner lists

# Looping through values inside nested lists
students = [
    ["Harry", 20],
    ["Sarah", 22],
    ["Bruno", 21]
]
 
for student in students:
    for value in student:
        print(value)

Output:

Harry
20
Sarah
22
Bruno
21

Nested Lists as Matrices (2D Lists)

Nested lists are useful when representing 2D data such as matrices.

# Matrix representation using nested lists
matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]
 
print(matrix[1][2])       # Row 1, Column 2

Output: