Chapter 7: Python Modules & Packages

1. What is a Module?

A module is a Python file (.py) containing reusable code (functions, variables, classes).

Key benefits:

Organize related code together
Promote code reuse
Prevent naming conflicts

my_module.py

# my_module.py
PI = 3.14159

def circle_area(radius):
    return PI * radius ** 2

def rectangle_area(length, width):
    return length * width

Exercise 1: Create a Module

Create a module named string_utils.py with:

A function reverse_string(s)
A function count_vowels(s)
Test it in another file

2. Importing Modules

1. Import Entire Module

import math
print(math.sqrt(25))

2. Import Specific Items

from math import sqrt, pi
print(sqrt(9))  # No math prefix

3. Import with Alias

import numpy as np
arr = np.array([1, 2, 3])

Exercise 2: Random Password Generator

Using the random module:

Create a function that generates 8-character passwords
Include uppercase, lowercase, and digits
Use random.choice()

import random
import string

def generate_password():
    chars = string.ascii_letters + string.digits
    return ''.join(random.choice(chars) for _ in range(8))

print(generate_password())  # e.g., "X7hL9pK2"

3. Packages

Package directory structure

Package Structure Example:

my_package/
├── __init__.py
├── module1.py
└── subpackage/
    ├── __init__.py
    └── module2.py

Importing from packages:

from my_package import module1
from my_package.subpackage import module2

Exercise 3: Create a Package

Create a package named shapes with:

Module circle.py with area/circumference functions
Module rectangle.py with area/perimeter functions
Import and test the package

4. Python Standard Library

Module	Purpose	Example Use
`os`	Operating system interactions	`os.listdir()`
`datetime`	Date/time handling	`datetime.now()`
`json`	JSON data handling	`json.loads()`
`sys`	System-specific parameters	`sys.argv`

Exercise 4: File Organizer

Using the os module:

List all files in current directory
Print only .txt files
Print file sizes

import os

for file in os.listdir('.'):
    if file.endswith('.txt'):
        size = os.path.getsize(file)
        print(f"{file} ({size} bytes)")

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