Rahul Gupta

Posted on Jul 16

Day 27/100: Nested Data Structures in Python

#python #programming #learning #100daysofcode

Welcome to Day 27 of the 100 Days of Python series!
Today, we’re diving into nested data structures — where things get structured, organized, and powerful.

When building real-world applications like APIs, databases, or configuration files, you’ll often use lists within dictionaries, dictionaries within lists, and more. Python makes this nesting easy and flexible.

Let’s explore how to create, access, and manipulate nested data structures like a pro. 🐍💼

📦 What You’ll Learn

What nested data structures are
How to build combinations like list in dict, dict in list, etc.
How to access deeply nested values
Best practices and real-world examples

🔄 What Are Nested Data Structures?

A nested data structure is simply one data structure inside another, like a list inside a dictionary or a dictionary inside a list.

🔹 1. List of Dictionaries

users = [
    {"name": "Alice", "age": 25},
    {"name": "Bob", "age": 30},
    {"name": "Charlie", "age": 22}
]

🔸 Accessing Items

print(users[0]["name"])  # Alice

Looping:

for user in users:
    print(user["name"])

🔹 2. Dictionary of Lists

grades = {
    "math": [90, 85, 88],
    "science": [92, 89, 94]
}

🔸 Accessing Values

print(grades["math"][1])  # 85

Adding a new grade:

grades["math"].append(95)

🔹 3. Dictionary of Dictionaries

users = {
    "alice": {"email": "alice@example.com", "age": 25},
    "bob": {"email": "bob@example.com", "age": 30}
}

🔸 Accessing Nested Values

print(users["bob"]["email"])  # bob@example.com

Modifying:

users["bob"]["age"] = 31

🔹 4. List of Lists

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]

🔸 Accessing Elements

print(matrix[1][2])  # 6

Looping:

for row in matrix:
    for val in row:
        print(val, end=" ")

📊 Real-World Examples

📋 1. JSON-like API Response

response = {
    "status": "success",
    "data": {
        "users": [
            {"id": 1, "name": "Alice"},
            {"id": 2, "name": "Bob"}
        ]
    }
}

Accessing Bob’s name:

print(response["data"]["users"][1]["name"])  # Bob

🧠 2. Quiz System Example

quiz = [
    {
        "question": "What is 2 + 2?",
        "options": [2, 3, 4, 5],
        "answer": 4
    },
    {
        "question": "What is the capital of France?",
        "options": ["London", "Berlin", "Paris", "Rome"],
        "answer": "Paris"
    }
]

Loop through questions:

for q in quiz:
    print(q["question"])
    print("Options:", q["options"])

✅ Best Practices for Nested Structures

✅ Use .get() to safely access nested keys:

  user.get("profile", {}).get("email", "Not Found")

✅ Use readable variable names when unpacking:

  for user in users:
      name = user["name"]
      age = user["age"]

✅ Keep nesting shallow when possible — deep nesting can make your code harder to maintain.

🧪 Bonus: Modifying Nested Structures

Updating a specific value:

users[1]["age"] = 35

Appending a new item to a nested list:

grades["science"].append(96)

🧠 Recap

Today you learned:

How to build and use nested data structures
Common combinations like lists of dicts and dicts of lists
How to access and modify deeply nested elements
Real-world use cases including API responses and quiz apps
Best practices for working with nested structures

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