# Những bước đầu tiên

Tệp tin FastAPI đơn giản nhất có thể trông như này:

```Python
{!../../docs_src/first_steps/tutorial001.py!}
```

Sao chép sang một tệp tin `main.py`.

Chạy live server:

<div class="termy">

```console
$ uvicorn main:app --reload

<span style="color: green;">INFO</span>:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

        "items:read items:write users:read profile openid"
    client_id: optional string. OAuth2 recommends sending the client_id and client_secret (if any)
        using HTTP Basic auth, as: client_id:client_secret
    client_secret: optional string. OAuth2 recommends sending the client_id and client_secret (if any)
        using HTTP Basic auth, as: client_id:client_secret
    """

    def __init__(

This includes, for example:

* Email notifications sent after performing an action:
    * As connecting to an email server and sending an email tends to be "slow" (several seconds), you can return the response right away and send the email notification in the background.
* Processing data:

Being able to use asynchronous functions in your tests could be useful, for example, when you're querying your database asynchronously. Imagine you want to test sending requests to your FastAPI application and then verify that your backend successfully wrote the correct data in the database, while using an async database library.

Let's look at how we can make that work.

## pytest.mark.anyio

# OpenAPI Webhooks

There are cases where you want to tell your API **users** that your app could call *their* app (sending a request) with some data, normally to **notify** of some type of **event**.

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps

Sería lo mismo que ir a:

```
http://127.0.0.1:8000/items/?skip=0&limit=10
```

Pero, si por ejemplo vas a:

```
http://127.0.0.1:8000/items/?skip=20
```

Los valores de los parámetros en tu función serán:

* `skip=20`: porque lo definiste en la URL
* `limit=10`: porque era el valor por defecto

## Parámetros opcionales

So, you will have to make sure your data is of the correct type. E.g. it is compatible with JSON, if you are returning a `JSONResponse`.

And also that you are not sending any data that should have been filtered by a `response_model`.

///

### More info

/// note | "Technical Details"

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

.mm",LTS:"HH.mm.ss",L:"DD/MM/YYYY",LL:"D MMMM YYYY",LLL:"D MMMM YYYY [pukul] HH.mm",LLLL:"dddd, D MMMM YYYY [pukul] HH.mm"},meridiemParse:/enjing|siyang|sonten|ndalu/,meridiemHour:function(e,a){return 12===e&&(e=0),"enjing"===a?e:"siyang"===a?11<=e?e:e+12:"sonten"===a||"ndalu"===a?e+12:void 0},meridiem:function(e,a,t){return e<11?"enjing":e<15?"siyang":e<19?"sonten":"ndalu"},calendar:{sameDay:"[Dinten puniko pukul] LT",nextDay:"[Mbenjang pukul] LT",nextWeek:"dddd [pukul] LT",lastDay:"[Kala wingi...

</pre>
```

</div>

It is **HIGHLY encouraged** that you write or copy the code, edit it and run it locally.

Using it in your editor is what really shows you the benefits of FastAPI, seeing how little code you have to write, all the type checks, autocompletion, etc.

---

## Install FastAPI

The first step is to install FastAPI.