← Python

Functions – Defining

def defines a named, reusable block of code that runs when called

What it does: A function is a reusable, named block of code, created with the def keyword: def greet():. The indented lines underneath — the function body — only run when the function is called by writing its name followed by parentheses: greet(). Defining a function doesn't run it; nothing happens until it's actually called, which is what lets the same code run many times from different places in a program.

Common mistakes: Forgetting the colon at the end of the def line (def greet() instead of def greet():) is the most common error. Another is defining a function but forgetting to call it — the code inside never runs on its own.

Class: _____________________ · Name: _____________________ · Date: _________

Free printable worksheet with full answer key — or add this module to a journey and assign it to your class.

🖨 Print Worksheet and Answer key of Functions – Defining (PDF)

Take this worksheet further — free with Cloodit

Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

What does def do?

Defines a new functionDeletes a function

Matches

❌ def greet() print('Hi')

↓

Error: Missing colon after def

Applying

Meanings

Term

def

Meaning

Keyword that creates (defines) a new function.

Practice

def greet():

Testing

Gaps

greet():

Check Answer

Spots

1def greet()

2 name = 'World'

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy

Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games

Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print

Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Teach this with your class →

Quick Questions

1. What does def do?

A. Defines a new function ✓

B. Deletes a function

def creates a new function — it doesn't run it

2. How do you call a function named greet?

A. def greet()

B. greet() ✓

def defines the function — to run it, write the name with parentheses

3. def say_hi():\n print('Hi')\nDoes this print anything?

A. No defining doesn't run it ✓

B. Yes prints Hi

Defining a function stores it — you must call it separately to run it

4. What goes at the end of a def line?

A. A semicolon ;

B. A colon : ✓

def lines end with a colon — the function body is indented below

5. Why use functions?

A. To reuse code without rewriting it ✓

B. To make code slower

Functions let you write code once and call it multiple times

Match the Pairs

def greet() print('Hi') → Error: Missing colon after def

Def say_hi(): print('Hi') → Error: 'def' is lowercase

def greet(): print('Hello') → Valid: Function defined

def greet(): print('Hi') greet() → Ok: Define then call

def say_hi(): print('Hi!') say_hi() → Output: Hi!

def say_hi(): print('Hi!') → Output: (nothing)

Key Term

def

Keyword that creates (defines) a new function.~~Function

Fill in the Blanks

1. def greet(): print('Hello!')

2. def greet(): print('Hello!')

3. def greet(): print('Hello!') greet()

4. def say_hi(): print('Hi!') say_hi()

5. def welcome(): print('Welcome!') welcome()

Spot the Error

Question 1

A def greet()

B name = 'World'

C print('Hello, ' + name)

D print('Goodbye!')

E greet()

Line A — Missing colon after the function definition

Question 2

A def greet():

B name = 'World'

C print('Hello, ' + name)

D print('Goodbye!')

E greet()

Line C — Code inside the function must be indented

Question 3

A Def greet():

B name = 'World'

C print('Hello, ' + name)

D print('Goodbye!')

E greet()

Line A — def must be lowercase

Question 4

A def greet:

B name = 'World'

C print('Hello, ' + name)

D print('Goodbye!')

E greet()

Line A — Missing parentheses: even with no parameters, use def greet():

Question 5

A def greet():

B print('Hello!')

D def greet()

Line D — To call a function, just use greet(): don't put def before it

For Teachers

Create a free class, add this module to a journey, and track who's stuck.

Create a free teacher account →

No credit card. No setup fee. Make a class and invite students in under three minutes.

For Students

Practice this topic interactively, track progress, and unlock badges.

Start Learning Free →

Have a class code?