Python Dictionaries

Lists keep things in order, indexed by position. This module covers Python’s other core collection: the dictionary, which stores data as key-value pairs, along with two related collection types: tuples and sets.

Why This Matters

Real data rarely comes as a flat, ordered list. It’s usually labeled: a username mapped to a profile, a product mapped to a price. A list only lets you look things up by position:

prices = [1.99, 2.49, 3.99]
prices[0]  # 1.99, but what does that even belong to?

A dictionary labels each value with a key, so you look things up by what they are, not where they sit in the collection:

prices = {"apple": 1.99, "banana": 2.49, "bread": 3.99}
prices["banana"]  # 2.49

Dictionaries are how Python represents that kind of labeled data, and you’ll use them constantly alongside lists.

What You’ll Learn

• How to create, read, and modify a dictionary
• The built-in methods for working with dictionary keys and values
• How to loop over a dictionary and use dictionary comprehension
• Tuples (immutable collections) and sets (unordered, unique collections)

Outcome

By the end of this module, you’ll be comfortable choosing between lists, dictionaries, tuples, and sets depending on what a problem actually calls for.

Let’s get started.