L8 Functions

Part 1: Creating and Calling Functions

We’ll start by learning how to define a function and how to run it in your code. This is called creating and calling a function. Think of it like writing your own command that the computer can understand and use again and again.

A function is a reusable block of code. You’ve already used built-in ones like print(). Now you’ll make your own. When you create (define) a function, you must always use the def keyword, followed by the name of the function, followed by brackets and a colon. As you already know from writing if / for / while etc, when you use a colon all following lines of code are indented!

📌 Function = Reusable code block that performs a task
📌 Function call = Tells the computer to run the function

Example

def greet():

    print ("Hello, welcome to Python!")

greet() 

# greet() calls the function and makes it run. Notice that we use brackets but that they are empty.

Part 2: Passing Parameters into Functions

Next, we’ll learn how to make functions more flexible by adding parameters. Parameters let you send information into a function so it can do different things depending on the input. If a function is expecting a parameter then you must send it one, otherwise you will get an error. Multiple parameters can also be sent, separating each one with a comma, for example: myfunction(parameter1, parameter2).

Example

def greet_user(name):

    return "Hello, " + name + "!"

message = greet_user("Alice")

print(message)

📍 Try changing "Alice" to another name. What happens?
📍 Add a second parameter and test what happens.

Part 3: Returning Values from Functions

Finally, we’ll explore how to use the return keyword. This allows a function to send back a result, which you can save in a variable and use elsewhere in your program. It’s a powerful way to make your functions more useful.

Example

def create_greeting(name):

    return f"Hello, {name}! Hope you're having a great day."

message = create_greeting("Bob")

print(message)

📌 Use return to send info back
📌 Store the returned value in a variable and use it later

🛑 Common Mistakes

❌ Defining a function but not calling it

❌ Printing inside the function instead of using return

❌ Forgetting the colon : after def

❌ Forgetting brackets () when calling a function