Modules, Packages and Virtual Environments

Real programs are built from many files and third-party libraries. Modules keep that organized and virtual environments keep it clean.

Importing

Python ships with a large standard library. Import a whole module or just the names you need.

import math
from datetime import date, timedelta

print(math.sqrt(81))          # 9.0
print(date.today())
print(date.today() + timedelta(days=7))

Your Own Module

Every .py file is a module. Create helpers.py with a function, then import it from main.py in the same folder.

# helpers.py
def slugify(text):
    return text.lower().strip().replace(" ", "-")

# main.py
from helpers import slugify

print(slugify("Introduction to Python"))

Virtual Environments

A virtual environment is a private folder of packages for one project. It prevents version clashes between projects.

python -m venv .venv
# Windows
.venv\Scripts\activate
# macOS / Linux
source .venv/bin/activate

pip install requests
pip freeze > requirements.txt

Using a Package

Once installed, import the package like any module. Keep a requirements.txt so another machine can install the same versions.

Practice

1. Import the random module and print a random number from 1 to 6.
2. Create a module with a function that converts Celsius to Fahrenheit.
3. Create a virtual environment and install requests.

Hands-on exercise

Create a module called money.py with a function format_naira(amount).
It should return a string like ₦1,250.00.
Then import it in main.py and print the result for 1250.

Recap

Modules split code into files, packages add outside code, and virtual environments keep each project's dependencies separate.