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Python function definition and calling

Introduction Reading Time: 10 min

Table of Contents

Description

A function in Python is a reusable block of code that performs a specific task. Functions help in modular programming, increase code reusability, and reduce redundancy.
You define a function using the def keyword, and you call it by its name followed by parentheses ()

Prerequisites

  • Understanding of Python syntax and indentation
  • Basics of variables and data types
  • Familiarity with expressions and control flow

Examples

Here's a simple program in Python:

# Defining a basic function
def greet():
    # This function simply prints a message
    print("Hello, welcome to Python!")

# Calling the function
greet()  # Output: Hello, welcome to Python!

# Function with parameters
def add(a, b):
    # This function adds two numbers
    return a + b

# Calling the function with arguments
result = add(10, 5)
print("Sum:", result)  # Output: Sum: 15

# Function with default parameter
def greet_user(name="Guest"):
    print(f"Hello, {name}!")

greet_user("Basha")  # Output: Hello, Basha!
greet_user()         # Output: Hello, Guest!

# Function with return type
def square(x):
    return x * x

print(square(4))  # Output: 16

Real-World Applications

Code modularization in large projects

Reusable logic like login verification, payment processing

Data analysis functions: clean, transform, and visualize

API creation: each endpoint often maps to a function

Game development: handling controls, physics, and rendering

Where topic Can Be Applied

Web development (Flask/Django): views and routes are functions

Data Science: analysis pipelines use custom-defined functions

Automation scripts: for repeated actions (e.g., file operations)

Machine Learning: feature extraction, training logic in functions

System programming: to handle modules or drivers

Resources

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Interview Questions

What is a function in Python?

How do you define and call a function?

What is the difference between a parameter and an argument?

Can a function return multiple values? How?

What is the purpose of default and keyword arguments?