Python Functions – Reusable Blocks of Code

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Day 6: Python Functions – Reusable Blocks of Code

Introduction

In Python, a function is a block of code that performs a specific task and can be reused anytime in your program.
Functions help make your code modular, organized, and easy to debug.

Python provides two types of functions:

  1. Built-in functions – e.g., len(), print(), type(), max()

  2. User-defined functions – created using the def keyword

1. Defining a Function

A function is defined using the def keyword followed by a name and parentheses.

Example:

def display():
    print("Hello, welcome to Python learning! Habbit2Code Online Coding Classes")

To call this function:

display()

Output:

Hello, welcome to Python learning! Habbit2Code Online Coding Classes

2. Function with Parameters/Arguments

Functions can take parameters (also called arguments) to pass data.

Example:

def add(a, b):
    result = a + b
    print("Sum =", result)

add(20, 5)

Output:

Sum = 25

3. Function with Return Value

Sometimes you may want the function to return a value.

Example:

def square(n):
    return n * n

result = square(6)
print("Square =", result)

Output:

Square = 36

4. Default Arguments

You can give default values to parameters.

Example:

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

greet("habbit2code@gmail.com")
greet()

 Output:

Hello habbit2code@gmail.com
Hello Guest

5. Keyword and Positional Arguments

You can pass arguments by position or by name.

Example:

def student(name, age):
    print(name, "is", age, "years old")

student("Ravi", 20)           # positional
student(age=18, name="Manu")  # keyword

6. Recursion (Function Calling Itself)

A function can call itself. This is called recursion.

Example:

def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n - 1)

print("Factorial =", factorial(5))

Output:

Factorial = 120

7. Practical Example

Let’s create a function to check whether a number is even or odd.

def check_number(num):
    if num % 2 == 0:
        print(num, "is Even")
    else:
        print(num, "is Odd")

check_number(7)

Output:

7 is Odd

8. Why Use Functions?

> Code reusability
> Easy debugging and maintenance
> Clear program structure
> Avoid repetition

Challenge for You

Create a Python program with a function that takes a list of numbers and returns only the even numbers.

Final Thoughts

Functions are like mini programs inside your main program.
They save time, make your code clean, and help you think logically.
In the next lesson, we’ll learn about lambda functions and modules to take this concept further.


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