/// tip

You'll see what other "things", apart from functions, can be used as dependencies in the next chapter.

///

Whenever a new request arrives, **FastAPI** will take care of:

* Calling your dependency ("dependable") function with the correct parameters.
* Get the result from your function.
* Assign that result to the parameter in your *path operation function*.

* Caddy (that can also handle certificate renewals)
* Nginx
* HAProxy

## Let's Encrypt { #lets-encrypt }

Before Let's Encrypt, these **HTTPS certificates** were sold by trusted third parties.

The process to acquire one of these certificates used to be cumbersome, require quite some paperwork and the certificates were quite expensive.

## Prérequis

FastAPI repose sur les épaules de géants :

* <a href="https://www.starlette.io/" class="external-link" target="_blank">Starlette</a> pour les parties web.
* <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> pour les parties données.

## Installation

<div class="termy">

```console
$ pip install fastapi

---> 100%
```

</div>

## Détails techniques

Les versions modernes de Python supportent le **code asynchrone** grâce aux **"coroutines"** avec les syntaxes **`async` et `await`**.

Analysons les différentes parties de cette phrase dans les sections suivantes :

* **Code asynchrone**
* **`async` et `await`**
* **Coroutines**

## Code asynchrone