Virtual Environments

Introduction

A virtual environment is an isolated Python installation for a single project. It has its own copy of pip and its own set of installed packages, completely separate from your system Python and other projects.

Without virtual environments, all packages from all projects are installed globally. This leads to version conflicts — Project A needs requests==2.28 but Project B needs requests==2.31, and they cannot both be satisfied at the same time.

Creating a Virtual Environment

Python's built-in venv module handles this.

# Create a virtual environment called .venv in the current directory
python -m venv .venv

The name .venv is the convention. The dot prefix hides it from directory listings by default on macOS and Linux.

Activating

You must activate the environment before using it. Once active, python and pip refer to the environment's versions.

# macOS / Linux
source .venv/bin/activate

# Windows (Command Prompt)
.venv\Scripts\activate

# Windows (PowerShell)
.venv\Scripts\Activate.ps1

Your prompt will change to show (.venv) when the environment is active.

Deactivating

deactivate

Checking You Are in the Right Environment

which python      # macOS/Linux — should show .venv/bin/python
where python      # Windows — should show .venv\Scripts\python.exe
pip list          # should only show packages for this project

Never Commit the .venv Folder

Add .venv to your .gitignore. It is large, OS-specific, and regeneratable from your dependency file.

# .gitignore
.venv/

Recreating an Environment

Because you never commit .venv, anyone cloning your project creates their own:

python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

Dependency files are covered in the next lesson.

Practice Exercises

• Create a new directory called test-project. Inside it, create a virtual environment.
• Activate it and run pip list — note that it starts nearly empty.
• Install requests into this environment. Confirm it is installed.
• Deactivate and run pip list again to confirm requests is not in the global environment.
• Delete the .venv folder and recreate it from scratch.