Dictionaries

Store and access data using key-value pairs for fast and organized data management.

Learn Python, JavaScript, Java and more with free interactive lessons, real projects and AI-powered help. Beginner-friendly.

Part of the free Python course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

A dictionary stores data in key-value pairs . Instead of accessing items by position (like lists), you access them by a unique key name.

There are two ways to access dictionary values:

Dictionaries are mutable — you can add new key-value pairs or update existing ones using the same syntax:

Use in to check if a key exists before accessing it:

Dictionaries can contain other dictionaries (or lists) as values. This is useful for organizing complex data.

Like list comprehension, you can create dictionaries in one line:

Lesson 8 done — you can now model real-world data in Python!

Dictionaries are how Python stores structured data — user profiles, API responses, config settings. You know how to create, access, update, loop, and nest them safely.

🚀 Up next: File Handling — learn to save data permanently so it survives after your program closes.

Practice quiz

How does a dictionary store data?

By index position
In key-value pairs
As a sorted set
As a fixed tuple

Answer: In key-value pairs. Dictionaries store data as key-value pairs, accessed by key name.

Which brackets create a dictionary?

Dictionaries use curly braces, e.g. {"name": "Alice"}.

What happens when you access a missing key with dict['missing']?

Returns None
Returns 0
Raises a KeyError
Adds the key

Answer: Raises a KeyError. Square-bracket access on a missing key raises a KeyError.

What does person.get('email', 'N/A') return if 'email' is missing?

None
'N/A'
KeyError
Empty string

Answer: 'N/A'. .get() returns the supplied default ('N/A') when the key is absent.

How do you add a new key 'age' with value 25 to dict person?

person.add('age', 25)
age

Answer: age. Assigning to a new key, person['age'] = 25, adds the pair.

Which loop gives you both keys and values?

for k in dict:
for v in dict.values():
for k, v in dict.items():
for i in dict.keys():

Answer: for k, v in dict.items():. .items() yields (key, value) pairs you can unpack in the loop.

Can a list be used as a dictionary key?

Yes, always
No, keys must be immutable
Only if it's empty
Only with .get()

Answer: No, keys must be immutable. Keys must be immutable (str, int, tuple); a list raises a TypeError.

What does {x: x**2 for x in range(1, 6)} create?

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}
{1, 4, 9, 16, 25}

Answer: {1: 1, 2: 4, 3: 9, 4: 16, 5: 25}. The dict comprehension maps each x (1-5) to its square.

If a dictionary literal has a duplicate key {'a': 1, 'a': 2}, what is the value of 'a'?

1
2
Error

Answer: 2. Keys are unique; the last value wins, so 'a' is 2.

What does len() return for {'name': 'Alice', 'age': 25, 'city': 'London'}?

Answer: 3. len() counts the number of key-value pairs: 3.