Dictionaries

Dictionaries

In this tutorial, we'll store labelled values as key-value pairs.

A dictionary stores labelled values. Each label is called a key.

student = {
    "name": "Ada",
    "score": 95,
    "passed": True,
}

Use dictionaries when you want to describe one thing with several pieces of information.

Reading Values

Use the key inside square brackets:

print(student["name"])
print(student["score"])

Output:

Ada
95

The key must match exactly. "Name" and "name" are different keys.

Updating Values

Dictionaries are mutable:

student["score"] = 98
student["grade"] = "A"

print(student)

This changes the score and adds a new key called "grade".

Using get()

If a key might be missing, get() is safer:

print(student.get("email"))
print(student.get("email", "No email saved"))

The second example gives a default value if "email" does not exist.

Looping Over a Dictionary

You can loop over keys and values:

for key, value in student.items():
    print(key, value)

Common Mistake

Do not use a list when your data needs labels:

student = ["Ada", 95, True]

This works, but it is not clear what each position means. A dictionary is more readable.

Practice

Create a dictionary for a film with title, year, rating, and watched status. Print a sentence using at least two keys.