Python Academy · Lesson

Dictionary Basics

Create dicts, access values by key, and iterate over them.

Lesson 1 of 414 steps

Dictionary Basics is a free Python Academy lesson on CoddyKit. This is lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Python Academy learning path, and your progress syncs across the web and the CoddyKit app. The Python Academy course includes 4 lessons in total.

Introduction

Dictionaries store key-value pairs with O(1) average lookup. Keys must be hashable; values can be anything.

Creating a Dict

d = {'name': 'Alice', 'age': 30} or d = dict(name='Alice', age=30). Keys must be unique and hashable.

d = {'name': 'Alice', 'age': 30}
print(d)

Accessing Values

d['name'] returns 'Alice'. If the key doesn't exist, it raises KeyError. Use d.get('key') for safe access.

d = {'name': 'Alice'}
print(d['name'])
print(d.get('missing', 'default'))

Adding and Updating

d['city'] = 'NYC' adds a new key. d['age'] = 31 updates an existing key. Dicts are mutable.

d = {'name': 'Alice'}
d['age'] = 30
print(d)

Deleting a Key

del d['key'] removes the key (KeyError if absent). d.pop('key') removes and returns the value.

d = {'a': 1, 'b': 2}
del d['a']
print(d)

Checking Key Existence

'name' in d returns True if 'name' is a key. Do NOT use d['name'] in a condition — that will raise KeyError.

d = {'name': 'Alice'}
print('name' in d)
print('age' in d)

Iterating Keys

for key in d: iterates over keys. for key in d.keys(): is equivalent. for val in d.values(): iterates values.

d = {'a': 1, 'b': 2}
for key in d:
    print(key, d[key])

Iterating Items

for k, v in d.items(): gives you both key and value in each iteration — the most common pattern.

d = {'a': 1, 'b': 2}
for k, v in d.items():
    print(f'{k}: {v}')

Nested Dictionaries

user = {'name': 'Alice', 'address': {'city': 'NYC'}}; user['address']['city'] gives 'NYC'.

user = {'name': 'Alice', 'address': {'city': 'NYC'}}
print(user['address']['city'])

Dict from Two Lists

dict(zip(keys, values)) creates a dict from two parallel lists.

keys = ['a', 'b', 'c']
vals = [1, 2, 3]
d = dict(zip(keys, vals))
print(d)

Counting with Dicts

Use a dict as a frequency counter: for ch in text: counts[ch] = counts.get(ch, 0) + 1

text = 'hello'
counts = {}
for ch in text:
    counts[ch] = counts.get(ch, 0) + 1
print(counts)

Quick Check

Which method safely returns a default value when a key is missing?

Answer it in the interactive lesson

Recap

Dicts: {key: value} with O(1) lookup. Use get() for safe access, in to check existence, items() to iterate, del/pop() to remove.

Keep Going

Great work! Move on to the next lesson to continue building your skills.

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Frequently Asked Questions

Is the “Dictionary Basics” lesson free?

Yes — the full text of “Dictionary Basics” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Python Academy course, upgrade to CoddyKit PRO. The Python Academy course includes 4 lessons in total.

What will I learn in “Dictionary Basics”?

Create dicts, access values by key, and iterate over them. You practise Python Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Python Academy?

No prior experience is required. Python Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 1 of 4.

How long does the “Dictionary Basics” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Python Academy lesson?

Yes. Every Python Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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