Lists, dictionaries, tuples, and sets can all contain each other. Real data is almost always shaped this way — a list of records, a record containing a list.

A list of dictionaries

This is the single most common shape you will meet. Think of it as a table: each dictionary is a row, each key a column.

people = [
    {"name": "Ada", "age": 36},
    {"name": "Grace", "age": 45},
    {"name": "Alan", "age": 41},
]

print(people[0])
print(people[0]["name"])

Read people[0]["name"] left to right: take the list, get item 0 (a dictionary), then get its "name" key.

Looping works exactly as you'd expect:

people = [
    {"name": "Ada", "age": 36},
    {"name": "Grace", "age": 45},
]

for person in people:
    print(f"{person['name']} is {person['age']}")

Note the single quotes inside the f-string — the outer string already uses double quotes, so switching quote style avoids ending the string early.

A dictionary of lists

Useful when one key owns many values.

classes = {
    "python": ["Ada", "Grace"],
    "rust": ["Alan"],
}

print(classes["python"])
print(classes["python"][1])

classes["rust"].append("Katherine")
print(classes["rust"])

classes["python"][1] is the same left-to-right read: get the list at "python", then item 1.

Going deeper

There is no limit to the nesting, though past two or three levels it gets hard to follow.

company = {
    "name": "Acme",
    "teams": [
        {"name": "backend", "size": 4},
        {"name": "design", "size": 2},
    ],
}

print(company["teams"][0]["name"])

total = 0
for team in company["teams"]:
    total += team["size"]
print(total)

Combining with comprehensions

Comprehensions get powerful on nested data — extracting one field from every record is a one-liner:

people = [
    {"name": "Ada", "age": 36},
    {"name": "Grace", "age": 45},
    {"name": "Alan", "age": 41},
]

names = [p["name"] for p in people]
print(names)

older = [p["name"] for p in people if p["age"] > 40]
print(older)

Try it yourself

Loop over the list of dictionaries, print each name, then print how many records there are.

Checkpoint

• A list of dictionaries is the standard shape for a table of records.
• Read data[0]["key"] left to right, one step at a time.
• Nested structures loop and comprehend just like flat ones.
• Watch your quote characters inside f-strings.