Project, Apps and First View

Django in brief

Django is a “batteries included” Python web framework: ORM for the database, template system, forms, authentication, admin interface, security protections… It is used for content sites, back offices, SaaS and APIs. This course uses Django 6.1 (which requires Python 3.12 or newer); the concepts presented are the same in the long-term support version 5.2 LTS.

Creating a project

python -m venv .venv && source .venv/bin/activate
python -m pip install Django            # latest stable version (6.1)
django-admin startproject config .     # the dot: creates the project in the current folder
python manage.py runserver              # http://127.0.0.1:8000

Resulting directory structure:

manage.py            project command tool
config/
    settings.py      configuration (apps, database, language...)
    urls.py          main URL table
    wsgi.py, asgi.py entry points for production servers

In settings.py, set LANGUAGE_CODE = "fr-fr" and TIME_ZONE = "Europe/Paris".

Creating an app

A project is a site; an app is a module that handles a feature (catalog, blog, accounts). A project contains several.

python manage.py startapp catalogue

Then declare it in config/settings.py:

INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    # ... apps provided by Django ...
    "catalogue",            # our app
]

First view

A view is a function that receives a request (HttpRequest) and returns a response (HttpResponse).

# catalogue/views.py
from django.http import HttpResponse


def accueil(request):
    return HttpResponse("<h1>Bienvenue dans le catalogue</h1>")


def detail_produit(request, pk):        # pk comes from the URL, already converted to int
    return HttpResponse(f"Produit n°{pk}")

Linking URLs to views

# catalogue/urls.py (file to create)
from django.urls import path
from . import views

app_name = "catalogue"                   # namespace for the app's URLs
urlpatterns = [
    path("", views.accueil, name="accueil"),
    path("produits/<int:pk>/", views.detail_produit, name="detail"),
]

# config/urls.py
from django.contrib import admin
from django.urls import include, path

urlpatterns = [
    path("admin/", admin.site.urls),
    path("catalogue/", include("catalogue.urls")),   # delegates everything starting with catalogue/
]

<int:pk> is a converter: it only accepts digits and passes an int to the view. The others: str (default, anything except /), slug (letters, digits, hyphens, underscores), uuid, path (also accepts /). /catalogue/produits/abc/ matches no pattern: Django returns 404.

The name parameter lets you generate URLs without hard-coding them: reverse("catalogue:detail", args=[3]) gives /catalogue/produits/3/.

The journey of a request

1. The browser requests /catalogue/produits/3/.
2. Django goes through config/urls.py in order, finds catalogue/, then continues in catalogue/urls.py with produits/3/.
3. The first matching pattern wins: Django calls detail_produit(request, pk=3).
4. The view returns an HttpResponse (often built from a model and a template).

This is the MTV architecture: the Model handles data, the Template presentation, the View logic. URL dispatching is handled by the framework.

Key takeaways

• startproject once, startapp per feature, without forgetting INSTALLED_APPS.
• View = function request → HttpResponse.
• path() + converters + name, and include() for each app.