Is the Dictionaries lesson free?

Yes. The first 5 lessons on PyRun are free forever — no signup, no card. Dictionaries runs real Python in your browser via Pyodide.

How long does the Dictionaries lesson take?

About 6 minutes end-to-end. It's a hands-on lesson — you read a paragraph, edit the code, and run it in the same tab.

Do I need to install Python to try the Dictionaries lesson?

No install required. PyRun runs real CPython in your browser via Pyodide (Python compiled to WebAssembly). Works on Chrome, Firefox, Safari, and Edge — desktop or mobile.

What level is the Dictionaries lesson?

Beginner level. No prior Python required — good starting point.

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Beginner·6 min·basics · dicts

Dictionaries

You’ll be able to

Store key-value pairs with dict literals {}
Look up, update, and delete entries safely
Iterate over keys, values, and items with .keys(), .values(), .items()
Use .get() to avoid KeyError when accessing missing keys

Why this matters

Dicts back every JSON API response, Django ORM row, and pandas record. Redis, MongoDB, and even Python's own class attributes are dicts under the hood. Fluency here is non-negotiable for backend or data roles.

Common pitfalls

Accessing a missing key with d[k] raises KeyError. Use d.get(k) or d.get(k, default) for safe lookups.
Using mutable objects like lists as keys. Only hashable types (str, int, tuple) work; lists raise TypeError.
Iterating for k in d and expecting values. That yields keys; use d.items() for pairs.

A dict maps a key to a value. Keys must be unique and immutable (strings, numbers, tuples).

Three things you'll use constantly

d[key] — read or write
d.get(key, default) — read without crashing if missing
d.items() — iterate over (key, value) pairs

Try it

Add three more items to prices.
Print the total cost of one of each fruit using sum(prices.values()).

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
The dict prices = {"apple": 30, "banana": 10, "mango": 80} maps fruit to rupees. Print the price of mango. Expected last line: 80.
Exercise 2
For the same prices dict, compute and print the total cost if you buy one of each fruit — expected: 120.
Exercise 3
From words = ["apple", "kiwi", "banana", "fig"], build a dictionary mapping each word to its length, then print the dictionary. Expected includes: {'apple': 5, 'kiwi': 4, 'banana': 6, 'fig': 3}.

← PreviousTuples & Sets Next →Truthiness & None

Dictionaries

You’ll be able to

Store key-value pairs with dict literals {}
Look up, update, and delete entries safely
Iterate over keys, values, and items with .keys(), .values(), .items()
Use .get() to avoid KeyError when accessing missing keys

Why this matters

Common pitfalls

Accessing a missing key with d[k] raises KeyError. Use d.get(k) or d.get(k, default) for safe lookups.
Using mutable objects like lists as keys. Only hashable types (str, int, tuple) work; lists raise TypeError.
Iterating for k in d and expecting values. That yields keys; use d.items() for pairs.

A dict maps a key to a value. Keys must be unique and immutable (strings, numbers, tuples).

Three things you'll use constantly

d[key] — read or write
d.get(key, default) — read without crashing if missing
d.items() — iterate over (key, value) pairs

Try it

Add three more items to prices.
Print the total cost of one of each fruit using sum(prices.values()).

Practice

3 graded exercises

Write the code, click Check. We’ll tell you exactly what to fix.

Progress0 / 3

Exercise 1
The dict prices = {"apple": 30, "banana": 10, "mango": 80} maps fruit to rupees. Print the price of mango. Expected last line: 80.
Exercise 2
For the same prices dict, compute and print the total cost if you buy one of each fruit — expected: 120.
Exercise 3
From words = ["apple", "kiwi", "banana", "fig"], build a dictionary mapping each word to its length, then print the dictionary. Expected includes: {'apple': 5, 'kiwi': 4, 'banana': 6, 'fig': 3}.