Comment une requête devient une réponse

Every page view is a round trip: the browser sends a request, your server does work, and a response travels back. Let us trace that journey.

A user clicks a link, and the browser sends an HTTP request. It carries the method, the URL path, and some headers describing the client.

Flask reads the path and finds the matching route. If no route matches, you get a 404 before any view function ever runs.

Once matched, Flask calls your view function. This is where your code runs: read input, do logic, and decide what to send back.

Inside the view, the request object holds everything the client sent. You import it from Flask to read details about the incoming call.

Your function returns a value, and that value becomes the response body. It can be text, HTML, or JSON depending on what you build.

Flask wraps your return value in a response object. That object bundles the body together with a status code and headers.

Every response carries a status code. A 200 means success, while a 404 or 500 signals that something went wrong along the way.

Response headers describe the body, like its content type and length. The browser reads them to know how to render what you sent.

Finally the browser receives the response, reads the headers, and paints the body on screen. The round trip is complete.

The rule is simple: each request gets exactly one response. Your view runs, returns once, and Flask ships that single reply back.

Trace the request cycle in your head, then answer.

You traced the cycle: request in, route match, view runs, response out. Knowing this flow makes every Flask bug far easier to find. 🔁