🧰 Functions and Modules in Python: A Practical Guide

🔍 Introduction

In Python, functions and modules are essential tools for writing clean, reusable, and maintainable code. Functions allow you to encapsulate logic for repeated use, while modules let you organize related code across multiple files or packages.

In this article, you'll learn:

• How to define and call functions
• The importance of parameters and return values
• Scope and lifetime of variables
• How to import and use modules
• Creating your own modules

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🧠 Why Use Functions and Modules?

• Avoid code duplication
• Improve readability
• Enable testing and debugging
• Facilitate collaboration and modular programming

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✅ 1. Functions in Python

➤ Defining a Function

def greet(name):
    print(f"Hello, {name}!")

➤ Calling a Function

greet("Alice")

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📥 Parameters and 📤 Return Values

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

result = add(5, 3)
print(result)  # Output: 8

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🎯 Default Parameters

def greet(name="Guest"):
    print(f"Hello, {name}!")

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🔄 Variable-Length Arguments

def sum_all(*args):
    return sum(args)

print(sum_all(1, 2, 3, 4))  # Output: 10

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🌐 Variable Scope

• Local Scope: Defined inside the function
• Global Scope: Defined outside any function

x = 5

def func():
    x = 10  # local
    print(x)

func()  # 10
print(x)  # 5

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📦 2. Modules in Python

Modules are simply Python files (.py) containing functions, variables, and classes.

➤ Importing a Module

import math

print(math.sqrt(16))  # Output: 4.0

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➤ Importing Specific Elements

from math import pi, sin

print(pi)           # Output: 3.14159...
print(sin(pi / 2))  # Output: 1.0

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➤ Creating Your Own Module

1. Create a file mymath.py:

def square(x):
    return x * x

2. Use it in another file:

import mymath

print(mymath.square(5))  # Output: 25

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📁 Built-in vs Third-Party Modules

• Built-in: math, os, random, datetime, etc.
• Third-party: Install using pip, e.g., requests, numpy, pandas.

pip install requests

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🧪 Practice Example: Temperature Converter

# temp_converter.py

def celsius_to_fahrenheit(c):
    return (c * 9/5) + 32

def fahrenheit_to_celsius(f):
    return (f - 32) * 5/9

# main.py

import temp_converter

print(temp_converter.celsius_to_fahrenheit(100))  # 212.0

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🔁 Summary

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🧩 Conclusion

Functions and modules are fundamental to writing organized Python code. They help you structure your code better, promote reusability, and make debugging easier. Start using functions to break problems into pieces and modules to share logic across files.

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🧠 Practice Ideas

1. Create a module for basic arithmetic operations.
2. Write a function that returns the factorial of a number.
3. Create a module that formats dates in different styles.