Python Functions

As you write more code, you’ll notice that some parts of your code repeat. Instead of writing the same thing again and again, we can group that code into something called a function.

Functions let you give a name to a block of code. Later, you can use that name to run the code whenever you want — as many times as you want!

Why Do We Need Functions?

To avoid repeating the same code again and again.
To make our code clean and easy to understand.
To organize code into smaller, manageable pieces.

Basic Syntax of a Function

This is how you define a simple function in Python:

def function_name():
    # block of code
    print("Hello!")

Explanation:

def is a keyword used to define a function.
function_name is the name you choose for your function (no spaces, only letters, numbers, and underscores).
() is where we can pass information (called parameters) — more on that below.
The code inside the function is written with indentation (usually 4 spaces).

How to Call (Use) a Function

Once the function is defined, you can use it like this:

def say_hello():
    print("Hello!")

say_hello()

Hello!

Explanation: The line say_hello() tells Python to run the code inside the function.

Functions with Parameters (Inputs)

You can also send information to a function by using parameters:

def greet(name):
    print("Hello, " + name + "!")

greet("Arjun")
greet("Bob")

Hello, Arjun!
Hello, Bob!

Explanation: The word you pass inside greet() goes into the name variable inside the function.

Functions That Return a Value

Sometimes you want a function to calculate and give back a value. For that, we use the return keyword:

def add(a, b):
    return a + b

result = add(3, 4)
print(result)

Explanation: The function add() calculates 3 + 4 and returns 7, which we print.

Different Types of Functions

No input, no return: Just does something like print
With input, no return: Takes input and prints result
With input and return: Takes input and gives back result

Examples of All Types

# No input, no return
def show_message():
    print("Welcome!")

# Input, no return
def greet_user(name):
    print("Hi, " + name)

# Input and return
def multiply(x, y):
    return x * y

# Using the functions
show_message()
greet_user("Zara")
print(multiply(3, 5))

Welcome!
Hi, Zara
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Conclusion

Functions are like mini-programs inside your main program. You can call them whenever you need them. This makes your code easier to read, write, and fix.