Virtual environments and packages (before the web modules)

By this point in the course you have been writing Python with whatever interpreter your template and editor use. For the final web chapters, you want an isolated environment and the right libraries installed cleanly.

Virtual environments

A virtual environment is a directory of packages for one project.

python3 -m venv .venv

Activate:

• macOS / Linux: source .venv/bin/activate
• Windows (cmd): .venv\Scripts\activate.bat
• Windows (PowerShell): .venv\Scripts\Activate.ps1

Deactivate: deactivate

Tip

After activating, run python --version and which python (or where python) to confirm you are inside the venv.

Installing web and HTTP dependencies

Your Classroom template may ship pyproject.toml or requirements.txt. Typical packages for the closing chapters:

• fastapi — web framework
• uvicorn — ASGI server
• pydantic — data validation (you already used it earlier; ensure it is installed here if needed)
• httpx — HTTP client

Example:

pip install fastapi uvicorn pydantic httpx

Or use pip install -r requirements.txt, uv sync, or Poetry, per your template.

Running the web server (preview)

Once app exists in a module (next chapters):

uvicorn app:app --host 0.0.0.0 --port 8000 --reload

First app = module name; second app = FastAPI() instance.

Implement

1. Create and activate .venv in your repo (if you have not already).
2. Install FastAPI, Uvicorn, HTTPX, and ensure Pydantic is available.
3. Confirm python -c "import fastapi, uvicorn, httpx, pydantic" succeeds.
4. Commit lockfiles / dependency files your instructor wants—not .venv itself.