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Setting Up: Virtual Environments and Installing Django  ›  Lesson

Virtual Environments

Virtual envs 12 minA virtual environment is a private folder of Python packages for one project, so each project can use its own versions without affecting the others.

Virtual Environments

You start the cookbook on the newest Django. Next month you pick up an older site that must stay on an earlier version. If both live in the same Python installation, installing one quietly replaces the other, and a project that worked yesterday breaks today. The fix takes one command, and you run it before anything else.

The rule

One project, one environment: packages never share a home.

A virtual environment is a folder that holds its own copy of Python's package directory. While it is active, python and pip point into that folder, so whatever you install lands there and nowhere else.

Python ships the tool for this, venv. From inside the project folder:

mkdir cookbook && cd cookbook
python3 -m venv .venv          # create it (use "python" on Windows)
source .venv/bin/activate      # activate on macOS / Linux
# .venv\Scripts\activate       # activate on Windows

Your prompt usually gains a (.venv) prefix to show which environment is live. Check it any time:

python -c "import sys; print(sys.prefix)"   # prints a path ending in .venv

To leave, run deactivate. The folder stays; activate it again next session.

Three habits keep this painless:

  • Name it .venv and keep it inside the project folder, so it is obvious which environment belongs to which project.
  • Never commit it. Add .venv/ to .gitignore; it is rebuilt from a list of requirements instead.
  • If an environment gets into a strange state, delete the folder and create a fresh one. It holds nothing you wrote.

Other tools, such as virtualenv, pipenv, poetry and uv, manage environments too. They differ in comfort, not in the idea.

The shortcut

Before any pip install, glance at the prompt: no (.venv), no install. Activation is the switch that decides where packages go.

First minutes of the cookbookStep 1 of 4

  1. Make the folder

    mkdir cookbook && cd cookbook. Everything for this project lives here.

The classic mistake is opening a new terminal, forgetting to activate, and installing into the system Python. The project then says "No module named django" even though you "just installed it".

Drills

Answer fast — trust the rule.

quick drill

Which command creates a virtual environment in a folder named .venv?

quick drill

Should the .venv folder be committed to Git?

quick drill

You open a new terminal and run pip install Django without activating. Where does Django go?

quick drill

How do you leave an active virtual environment?

Remember

  • One project, one environment: packages never share a home.
  • No (.venv) in the prompt, no install.
  • Trap: a new terminal is not activated, and .venv never goes into Git.

Practice — level up

0/1 solved

Write your answer, then compare it with a rubric and a model answer.

ExplainTwo projects, two Djangos

You maintain an old site that needs Django 4.2 and are starting the cookbook on Django 5.2. Explain what goes wrong if you install both into your system Python, and how virtual environments fix it. Include the commands to create and activate one.