Python Functions

Functions are reusable blocks of code that perform a specific task. Functions help programmers avoid writing the same code again and again.

Why Functions are Important?

Functions reduce repeated code.
Functions make programs organized.
Functions improve readability.
Functions make debugging easier.
Functions are reusable in multiple places.

Creating a Function

In Python, functions are created using the def keyword.

def greet():
    print("Welcome to CodeVyro")

Here:

def is used to define a function.
greet is the function name.
Parentheses () are required.
Indented code belongs to the function.

Calling a Function

A function runs only when it is called.

def greet():
    print("Welcome to CodeVyro")

greet()

Output

Welcome to CodeVyro

When Python sees greet(), it executes the function code.

Function with Parameters

Parameters allow functions to receive data.

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

greet("Rahul")

How this Works?

Step 1: Function accepts parameter name.

Step 2: Value "Rahul" is passed into the function.

Step 3: Python prints the message.

Output

Hello Rahul

Function with Multiple Parameters

def student(name, marks):
    print("Name:", name)
    print("Marks:", marks)

student("Ali", 95)

Output

Name: Ali
Marks: 95

Return Statement

The return keyword sends a value back from a function.

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

result = add(10, 20)

print(result)

How this Program Works?

Function receives values 10 and 20.
Python adds both numbers.
return sends result back.
Returned value gets stored in variable result.

Output

Difference Between print() and return

print() displays output on screen.
return sends value back to the caller.
Returned values can be stored and reused.

Default Parameters

Functions can have default values.

def greet(name = "Guest"):
    print("Hello", name)

greet()

greet("Rahul")

Output

Hello Guest
Hello Rahul

If no value is passed, Python uses the default value.

Keyword Arguments

Arguments can be passed using parameter names.

def student(name, marks):
    print(name)
    print(marks)

student(marks = 90, name = "Ali")

Output

Ali
90

Arbitrary Arguments (*args)

*args allows multiple values to be passed into a function.

def numbers(*data):
    print(data)

numbers(10, 20, 30, 40)

Output

(10, 20, 30, 40)

Variable Scope

Variables created inside functions are local variables.

def test():
    x = 100
    print(x)

test()

Variable x exists only inside the function.

Global Variables

Variables created outside functions are global variables.

name = "Python"

def show():
    print(name)

show()

Output

Python

Recursion

Recursion happens when a function calls itself.

def countdown(n):
    if n == 0:
        print("Finished")

    else:
        print(n)
        countdown(n - 1)

countdown(5)

Output

5
4
3
2
1
Finished

Built-in Functions

Python already provides many built-in functions.

print(len("Python"))

print(max(10, 50, 20))

print(min(10, 50, 20))

Output

6
50
10

Real Life Example

This example creates a simple calculator function.

def calculator(a, b):
    print("Addition:", a + b)
    print("Subtraction:", a - b)
    print("Multiplication:", a * b)

calculator(10, 5)

Output

Addition: 15
Subtraction: 5
Multiplication: 50

Summary

Functions are reusable blocks of code.
Functions are created using def keyword.
Functions run only when called.
Parameters allow passing data.
return sends values back.
Functions improve readability and reusability.
Python supports recursion and built-in functions.