Working With Nested Data

Real-world data is rarely flat. When you fetch data from an API or read a JSON file, you'll encounter nested structures — lists containing dictionaries, dictionaries containing lists, and combinations of both.

Lists of Dictionaries

This is perhaps the most common pattern. Each item in the list is a dictionary representing one record:

users = [
    {"name": "Alice", "age": 30},
    {"name": "Bob", "age": 25},
    {"name": "Charlie", "age": 35}
]

To access a specific user's name, chain the accesses:

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

First, users[0] gets the first dictionary. Then ["name"] gets the name value from that dictionary.

Looping Through Nested Data

To process all users, loop through the list. Each iteration gives you one dictionary:

for user in users:
    print(f"{user['name']} is {user['age']} years old")

Output:

Alice is 30 years old
Bob is 25 years old
Charlie is 35 years old

Inside the loop, user is a dictionary, so you access its values with keys.

Dictionaries Containing Lists

The nesting can go the other way too:

classroom = {
    "teacher": "Ms. Smith",
    "students": ["Alice", "Bob", "Charlie"],
    "room": 101
}

To loop through the students:

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

First, classroom["students"] gets the list. Then the for loop iterates over that list.

Deeper Nesting

Data can nest multiple levels deep:

company = {
    "name": "TechCorp",
    "departments": [
        {
            "name": "Engineering",
            "employees": ["Alice", "Bob"]
        },
        {
            "name": "Marketing",
            "employees": ["Charlie", "Diana"]
        }
    ]
}

# Get first department's first employee
print(company["departments"][0]["employees"][0])  # Alice

Read this left to right: get departments (a list), get index 0 (a dictionary), get employees (a list), get index 0 (a string).

Tips for Nested Data

When working with complex structures:

Print intermediate values to understand the shape
Work from outside in — access one level at a time
Use descriptive variable names in loops to track what you're working with

# Clear naming helps
for department in company["departments"]:
    for employee in department["employees"]:
        print(f"{employee} works in {department['name']}")

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