Programming · StudentHub Lesson

Functions

Learn how to organize code into reusable blocks called functions with parameters and return values.

17 minBeginner

What you will learn

Define a function using def in Python
Pass parameters into a function
Return values from a function
Understand variable scope inside functions
Explain why functions make code reusable

Watch the lesson

Python for Beginners – Full Course [Programming Tutorial] · freeCodeCamp.org

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Topic notes

Main Idea

Functions are reusable blocks of code that perform a specific task, making programs organized and avoiding repetition.

Key Concepts

Functions are defined with the def keyword
Parameters let you pass data into a function
The return statement sends a value back to the caller
Variables defined inside a function have local scope

Definitions

Function: a named, reusable block of code that performs a task
Parameter: a variable listed in a function's definition
Return value: the output a function sends back

Syntax

```python

def greet(name):

return "Hello, " + name

message = greet("Sam")

print(message)

```

Examples

A function add(a, b) that returns a + b
A function is_even(num) that returns True or False

Common Mistakes

Forgetting to call the function with ()
Forgetting the return statement, causing None to be returned
Confusing parameters with arguments

Key concepts

Function definition with defParameters and argumentsReturn statementVariable scope

Important terms

Function: A reusable, named block of code that performs a specific task
Parameter: A variable used to pass data into a function
Return value: The result a function sends back to the code that called it

Worked examples

Problem

Write a function that adds two numbers

1. def add(a, b):
2. return a + b
3. print(add(2, 3))

Answer: 5

Quick revision

Functions are defined with def
Parameters pass data into functions
return sends a value back
Functions avoid repeating code
Local variables only exist inside their function

Check your understanding

Question 1 · Multiple choice

Which keyword defines a function in Python?

Question 2 · Multiple choice

What does the return statement do?

Question 3 · True or false

A function must always return a value.

Question 4 · Short answer

What is a parameter?

Question 5 · Short answer

Write a function call for a function named square that takes 4.

Done with Functions?

Loops Lists & Arrays