Lesson 9: Modules and Packages

What Are Modules?

A module is simply a Python file that contains functions, variables, or classes. Modules help you organize code into logical units and reuse functionality across multiple programs.

Creating a Module

Create a file named mymath.py:

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

def subtract(a, b):
    return a - b

Importing a Module

import mymath

print(mymath.add(3, 5))

Importing Specific Functions

from mymath import add

print(add(10, 20))

Built‑in Python Modules

Python includes a large standard library. Some common modules:

• math — mathematical functions
• random — random numbers
• datetime — dates and times
• os — operating system utilities

import math
print(math.sqrt(16))   # 4.0

What Are Packages?

A package is a collection of modules organized in folders. A package must contain an __init__.py file (even if empty) to be recognized by Python.

Package Structure Example

mypackage/
    __init__.py
    math_tools.py
    string_tools.py

Importing from a Package

from mypackage.math_tools import add

Installing External Packages

You can install third‑party packages using pip:

pip install requests

Using an Installed Package

import requests

response = requests.get("https://api.github.com")
print(response.status_code)

Why Modules and Packages Matter

• They keep code organized and maintainable.
• They allow reuse across multiple projects.
• They enable collaboration and large‑scale application development.
• They give access to Python’s huge ecosystem of libraries.

Next Steps

Now that you understand modules and packages, you’re ready to learn how Python reads and writes files in Lesson 10: File Handling (read/write).

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