Lesson 12: Virtual Environments & Packages

⏱ ~35 min Lesson 12 of 14 💚 Free

What You'll Learn

Create and activate virtual environments with venv
Install, upgrade, and uninstall packages with pip
Generate and use requirements.txt for reproducible environments
Understand the Python package ecosystem and PyPI

The Dependency Problem

Without virtual environments, every Python project on your machine shares the same global package pool. Project A needs requests 2.28, Project B needs requests 2.31 — they can't coexist. Virtual environments isolate each project's dependencies.

venv

python -m venv .venv — Creates a virtual environment in the .venv folder

Windows: .venv\Scripts\activate | macOS/Linux: source .venv/bin/activate

deactivate — Exit the virtual environment

Always add .venv/ to your .gitignore file. Never commit the virtual environment folder.

pip and requirements.txt

pip install requests — install latest version

pip install requests==2.31.0 — install specific version

pip freeze > requirements.txt — save all installed packages and versions

pip install -r requirements.txt — install all dependencies from the file (used to reproduce the environment)

Quick Check

1. Why are virtual environments necessary?

Python requires them for all projects

They isolate project dependencies so different projects can use different package versions

They make Python programs run faster

They are required by pip to install packages

2. What command creates a virtual environment in a folder called .venv?

pip install .venv

python -m venv .venv

virtualenv --new .venv

python create .venv

3. What does pip freeze > requirements.txt do?

Deletes all installed packages

Writes all currently installed packages and their exact versions to requirements.txt

Installs packages listed in requirements.txt

Updates all packages to their latest versions

4. Should you commit the .venv folder to Git?

Yes, so teammates get the same packages automatically

No — add .venv/ to .gitignore and commit requirements.txt instead

Only if the project is public

Yes, but only the Lib/ subfolder