Day 18: Nested Data Structures — Data Inside Data!

What's Nested Data?

Think of your house. House has rooms. Rooms have cupboards. Cupboards have drawers. Drawers have items. You go layer by layer to find what you need. Nested data works exactly the same — a dictionary can contain a list, which can contain more data, all stacked inside each other!

Dictionary Containing a List

student = {
    "name": "Rohith",
    "skills": ["Python", "SQL"]
}

student is a dictionary. Inside it, "skills" holds a list. One structure living inside another!

Accessing Nested Data

print(student["name"])         # Rohith
print(student["skills"])       # ['Python', 'SQL']
print(student["skills"][0])    # Python
print(student["skills"][1])    # SQL

Go one layer at a time! First ["skills"] gets the list. Then [0] gets the first item in that list. Like going House → Room → Cupboard → Item!

Real World Connection

Your Instagram profile is nested data — profile dictionary contains a list of posts, each post contains a list of comments, each comment contains a username and text. When Swiggy shows your order, it's a dictionary with your items list, each item having its own name and price. All of it is nested!

List of Dictionaries

students = [
    {"name": "Rohith", "age": 21},
    {"name": "Priya", "age": 20},
    {"name": "Sam", "age": 22}
]

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

Output: Rohith, Priya, Sam. A list of dictionaries — this is exactly how apps store multiple users, multiple products or multiple posts!

Common Mistakes

Mistake 1 — Stopping too early.

print(student["skills"])      # gets whole list — ['Python', 'SQL']
print(student["skills"][0])   # gets first item — Python

Mistake 2 — Wrong key name.

student["skill"]    # WRONG — key is "skills" not "skill"!
student["skills"]   # CORRECT

Mini Challenge

Quick Quiz

Q: How do you get "Python" from student = {"skills": ["Python", "SQL"]}? A: student["skills"][0] — first the key, then the position!

Q: What is a list of dictionaries useful for? A: Storing multiple similar items — users, products, posts!

Q: What's the rule for accessing nested data? A: One layer at a time — go step by step!

Key Takeaways