Reach inside collections.
One level at a time.

Apps often store structured data as lists of dictionaries or dictionaries whose values are lists.

01 Learn02 Try03 Predict

01 Learn

Collections can contain other collections.

Apps often store structured data as lists of dictionaries or dictionaries whose values are lists.

student = {"name": "Ana", "scores": [8, 9]}
print(student["scores"][1])

First the key selects the inner list; then index 1 selects its second score.

Try changing one value, then explain which part of the collection changed and why.

↳

Keep this in mind: Read the collection operation before predicting the result.

Try it

students = [
    {"name": "Ana", "scores": [8, 9]},
    {"name": "Marko", "scores": [7, 10]}
]

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

Run the example, then change one value and observe the result.

A list of dictionaries

users = [{"name": "Ana"}, {"name": "Marko"}]
print(users[1]["name"])

Use a numeric index to choose a dictionary from the list, then a key to choose its value.

A dictionary of lists

groups = {"python": ["Ana", "Marko"]}
print(groups["python"][0])

Use a key to choose the list, then an index to choose an item inside it.

02 Try

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03 Predict

What will this program print?

Read each operation before choosing an answer.

courses = {
    "python": ["Ana", "Marko"],
    "django": ["Jelena"]
}

print(courses["python"][1])
print(len(courses["django"]))

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04 Understanding Check

What will this program print, and why? Explain the list index, dictionary keys, and inner list length.

projects = [
    {"name": "Website", "tasks": ["Design", "Code"]},
    {"name": "App", "tasks": ["API", "Testing", "Deploy"]}
]

print(projects[1]["name"])
print(projects[0]["tasks"][1])
print(len(projects[1]["tasks"]))