How to Create a Simple Function in Python

A Python function lets you group code into a reusable block. This page shows the simplest working pattern first: define a function, then call it.

You will also learn how to avoid common beginner mistakes like missing parentheses or bad indentation. Once this basic pattern makes sense, it becomes much easier to learn Python functions explained, parameters, and return values.

Quick answer

def say_hello():
    print("Hello")

say_hello()

Use def to create the function, indent the code inside it, then call the function by writing its name with parentheses.

What this page helps you do

Create your first Python function
Understand the basic function pattern
Run the function by calling it
Avoid beginner mistakes like missing parentheses or bad indentation

Start with the basic function structure

A function is a reusable block of code.

In Python, you create a function with the def keyword:

def function_name():
    # code goes here

This pattern has four important parts:

def starts the function definition
function_name is the name you choose
() means the function takes no inputs for now
: starts the function body

The code inside the function must be indented.

Create and call a simple function

Here is a simple function that prints a message:

def say_hello():
    print("Hello")

say_hello()

Expected output:

Hello

This example does two things:

It defines the function say_hello
It calls the function with say_hello()

A very important rule for beginners:

Defining a function does not run it
Nothing happens until you call the function

If you only write this:

def say_hello():
    print("Hello")

you will see no output, because the function was created but never called.

Understand each line

Look at the same example again:

def say_hello():
    print("Hello")

say_hello()

Here is what each line does:

def say_hello(): starts the function definition
say_hello is the function name
: tells Python that the function body starts next
print("Hello") is inside the function because it is indented
say_hello() runs the code inside the function

You can test that the function exists by printing its name without calling it:

def say_hello():
    print("Hello")

print(say_hello)
print(type(say_hello))

You will see that Python treats the function as an object:

<function say_hello at 0x...>
<class 'function'>

This is why say_hello and say_hello() are different:

say_hello refers to the function
say_hello() calls the function

Choose a good function name

A good function name should describe what the function does.

Use:

lowercase letters
underscores between words
action-based names

Good examples:

print_name
show_menu
get_total

Avoid vague names like:

thing
stuff
do_stuff

Also avoid names that conflict with Python built-ins, such as list or print. Reusing built-in names can cause confusing bugs later.

Add a second simple example

Functions are useful because you can reuse them.

Without a function, you might repeat the same line many times:

print("Welcome!")
print("Welcome!")
print("Welcome!")

With a function, you write the code once and call it whenever you need it:

def show_welcome():
    print("Welcome!")

show_welcome()
show_welcome()
show_welcome()

Expected output:

Welcome!
Welcome!
Welcome!

This is one of the main reasons functions are helpful:

less repeated code
easier to update later
clearer program structure

Common beginner mistakes

Here are some common problems when creating a simple function.

Forgetting the colon

This is wrong:

def say_hello()
    print("Hello")

Python expects a colon after the function header.

Correct version:

def say_hello():
    print("Hello")

If you get this wrong, see how to fix SyntaxError from a missing colon.

Forgetting to indent the function body

This is wrong:

def say_hello():
print("Hello")

The body of the function must be indented.

Correct version:

def say_hello():
    print("Hello")

If Python says it expected an indented block, read how to fix IndentationError: expected an indented block.

Using the function name without `()`

This does not call the function:

def say_hello():
    print("Hello")

say_hello

To run the function, you must add parentheses:

def say_hello():
    print("Hello")

say_hello()

Calling the function before it is defined

In a Python file, the function usually needs to be defined before you call it.

Wrong order:

say_hello()

def say_hello():
    print("Hello")

Correct order:

def say_hello():
    print("Hello")

say_hello()

Expecting a printed value to be returned

This function prints a message:

def say_hello():
    print("Hello")

But it does not return a value.

That means this:

result = say_hello()
print(result)

will output:

Hello
None

print("Hello") shows text on the screen
the function returns None because there is no return

If this part feels confusing, the next step is learning return values in Python functions.

What to learn next

Once you can create and call a simple function, the next step is making functions more useful.

You can learn how to:

pass inputs with function parameters and arguments in Python
send a result back with return values in Python functions
make inputs optional with default arguments in Python