Set Up a Virtual Environment

Every web project in this course lives in its own folder with its own virtual environment. A virtual environment (or venv) is a private copy of Python's package area, so the Flask version used by your tiffin app cannot clash with the Django version used by your library project.

In this lesson you will check your Python version, create and activate a venv, install Flask and Django, save the exact versions in requirements.txt, and set up VS Code to use the right Python. You will also meet uv, a fast modern tool that many teams now use for the same job.

Why a virtual environment?

Without a venv, pip install puts packages into one shared place for your whole computer. That causes three problems:

• Two projects need different versions of the same package, and only one can be installed.
• You forget which packages a project needs, so it fails on a friend's laptop or on the server.
• Upgrading a package for one project silently breaks another.

A venv solves all three. It is just a folder (we call it .venv) with its own python and pip. You can delete it and recreate it at any time, which is why it never goes into Git.

Check Python first

Django 6.1 needs Python 3.12 or newer; Flask 3.1 needs 3.9 or newer. Check what you have:

python --version

Python 3.14.8

On Windows, if python opens the Microsoft Store or is not found, install Python from python.org (or with the Python install manager, which gives you the py command) and open a new terminal. On Linux and macOS the command is often python3. See Install Python & Set Up for full steps.

Create and activate a venv

Make a project folder and create the venv inside it. The second venv below is the module name; .venv is the folder name.

mkdir pune-tiffin
cd pune-tiffin
python -m venv .venv

Now activate it. Activation changes your terminal so that python and pip point into .venv. The command depends on your shell:

After activation your prompt starts with (.venv). Type deactivate to leave. You must activate again every time you open a new terminal.

To confirm that Python is really running from the venv, ask it where it lives:

python -c "import sys; print(sys.prefix)"

C:\Users\aarav\projects\pune-tiffin\.venv

If the path does not end in .venv, you forgot to activate, and pip would install into the wrong place.

Install Flask and Django

With the venv active, install both frameworks. Using python -m pip instead of plain pip guarantees you use the pip that belongs to the active Python.

python -m pip install flask django

Successfully installed asgiref-3.13.0 blinker-1.9.0 click-8.5.0 django-6.1.2 flask-3.1.3 itsdangerous-2.2.0 jinja2-3.1.6 markupsafe-3.0.4 sqlparse-0.6.0 tzdata-2026.6 werkzeug-3.1.9

Two names became eleven packages. Flask brought Werkzeug (requests, responses and the dev server), Jinja2 (templates), Click (the flask command), itsdangerous (signed cookies) and Blinker (signals). Django brought asgiref (async support) and sqlparse; on Windows it also adds tzdata, because Windows has no built-in time zone database.

Check the versions:

flask --version
python -m django --version

Python 3.14.8
Flask 3.1.3
Werkzeug 3.1.9
6.1.2

In real projects you usually install only one of the two frameworks per venv. We install both here because this course uses both.

Pin versions in requirements.txt

When the project works, save the exact versions so anyone (including your server) can recreate the same environment:

python -m pip freeze > requirements.txt
python -m pip install -r requirements.txt

The first line writes lines such as Django==6.1.2 and Flask==3.1.3 into the file. The second line, run on another machine inside a fresh venv, installs exactly those versions. Commit requirements.txt to Git, and add .venv/ to your .gitignore.

A faster option: uv

uv is a newer tool that creates venvs and installs packages much faster than pip. Install it by following its official guide at https://docs.astral.sh/uv/, then:

uv venv
uv pip install flask django

uv venv creates .venv and uv pip install works like pip. For bigger projects, uv init creates a pyproject.toml, uv add django records the dependency and installs it, and uv run python manage.py runserver runs a command inside the project's environment without activating anything. Both pip and uv are fine for this course; pick one and stay consistent within a project.

Your editor

In VS Code, install the Python extension, open the project folder, press Ctrl+Shift+P and choose Python: Select Interpreter, then pick the one inside .venv. New terminals inside VS Code will then activate the venv for you, and the editor will find Flask and Django for auto-completion.

A clean project folder now looks like this:

pune-tiffin/
  .venv/              (never commit this)
  .gitignore          (contains .venv/)
  requirements.txt
  app.py              (your Flask app, next lesson)

Common mistakes

• Installing before activating. Packages go into the global Python and the project cannot find them later. Check for (.venv) in the prompt.
• Committing .venv to Git. It is large and tied to your computer. Commit requirements.txt instead.
• Mixing pip and python from different places. Use python -m pip to be sure.
• Using a Python that is too old. Django 6.1 will not install on Python 3.11 or older; pip then picks an older Django or fails.

Key points

• A virtual environment gives each project its own packages and versions.
• Create one with python -m venv .venv and activate it before installing anything.
• Install with python -m pip install flask django; check versions with flask --version and python -m django --version.
• pip freeze > requirements.txt pins versions; pip install -r requirements.txt recreates them.
• uv is a fast alternative (uv venv, uv pip install, uv add); keep .venv out of Git.

mkdir jaipur-library
cd jaipur-library
python -m venv .venv
source .venv/bin/activate        # Windows PowerShell: .venv\Scripts\Activate.ps1
python -m pip install django
python -m pip freeze > requirements.txt
deactivate
rm -rf .venv                     # Windows PowerShell: Remove-Item -Recurse -Force .venv
python -m venv .venv
source .venv/bin/activate
python -m pip install -r requirements.txt
python -m django --version

6.1.2