Nested Data Structures

Sometimes one data structure is not enough.

Real programs often store complex data such as:

• A student with many subjects
• A product with many details
• A class with many students
• A store with many products

To do this, Python allows one data structure inside another.

This is called nesting.

What Does Nested Mean?

Nested means placed inside something else.

Examples:

• A list inside a list
• A dictionary inside a dictionary
• A list inside a dictionary
• A dictionary inside a list

Why Nested Data Matters

Nested data helps you organize real information in a clean way.

Instead of many random variables, related data stays together.

List Inside a List

numbers = [
    [1, 2, 3],
    [4, 5, 6]
]

print(numbers)

Output

[[1, 2, 3], [4, 5, 6]]

Access Nested List Items

Use two indexes.

print(numbers[0][1])
print(numbers[1][2])

Output

2
6

Explanation:

• numbers[0] = first inner list
• numbers[0][1] = second item inside first list

Dictionary Inside a Dictionary

user = {
    "name": "Tom",
    "address": {
        "city": "New York",
        "country": "USA"
    }
}

print(user["address"]["city"])

Output

New York

List Inside a Dictionary

student = {
    "name": "Sara",
    "scores": [80, 90, 75]
}

print(student["scores"])
print(student["scores"][1])

Output

[80, 90, 75]
90

Dictionary Inside a List

students = [
    {"name": "Tom", "score": 85},
    {"name": "Sara", "score": 92}
]

print(students[0]["name"])
print(students[1]["score"])

Output

Tom
92

Updating Nested Data

You can change values inside nested data.

student = {
    "name": "Sara",
    "scores": [80, 90, 75]
}

student["scores"][0] = 100

print(student)

Output

{'name': 'Sara', 'scores': [100, 90, 75]}

Loop Through Nested Data

students = [
    {"name": "Tom", "score": 85},
    {"name": "Sara", "score": 92}
]

for student in students:
    print(student["name"], student["score"])

Output

Tom 85
Sara 92

Real Example: Store Products

products = [
    {"name": "Laptop", "price": 900},
    {"name": "Phone", "price": 500}
]

for product in products:
    print(product["name"], product["price"])

Output

Laptop 900
Phone 500

Code Along

classroom = {
    "teacher": "Maya",
    "students": ["Tom", "Sara", "John"]
}

print(classroom["teacher"])
print(classroom["students"][0])

Output

Maya
Tom

Mini Challenge

Build a movie collection.

Steps:

• Create a list of dictionaries with 2 movies
• Each movie should have:
  title, year
• Print the first movie title
• Print the second movie year
• Loop through all movies and print title and year

Expected output:

Inception
2020
Inception 2010
Avatar 2020

Real World Use Case

Programs use nested data for APIs, shopping carts, user profiles, dashboards, games, and databases.

Quiz

1. What does nested mean?
2. How do you access a list inside a dictionary?
3. Can dictionaries be stored in a list?
4. Why is nested data useful?

Assignment

Create a dictionary for a school. Add a list of students inside it. Print the school name and all student names.

Summary

You learned how Python stores data structures inside other data structures and how nested data is used in real programs.