ファイル名が `main.py` である場合、以下の方法でアプリケーションを実行します。

<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)
```

</div>

ブラウザで <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a> を開きます。

次のようなシンプルなページが表示されます。

<img src="/img/tutorial/websockets/image01.png">

<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)
```

</div>

Und öffnen Sie die Dokumentation unter <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

🔜, 🏃 `uvicorn` ⏮️ 👑 📱, 🚥 👆 📁 `main.py`, ⚫️ 🔜:

<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)
```

</div>

&amp; 📂 🩺 <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

👆 🔜 👀 🏧 🛠️ 🩺 👑 📱, 🔌 🕴 🚮 👍 _➡ 🛠️_:

<div class="termy">

```console
$ OPENAPI_URL= uvicorn main:app

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

</div>

그리고 `/openapi.json`, `/docs` 또는 `/redoc`의 URL로 이동하면 `404 Not Found`라는 오류가 다음과 같이 표시됩니다:

```JSON
{
    "detail": "Not Found"
}

<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)
<span style="color: green;">INFO</span>:     Started reloader process [28720]
<span style="color: green;">INFO</span>:     Started server process [28722]
<span style="color: green;">INFO</span>:     Waiting for application startup.

<font color="#4E9A06">INFO</font>:     Will watch for changes in these directories: [&apos;/home/user/code/awesomeapp&apos;]
<font color="#4E9A06">INFO</font>:     Uvicorn running on <b>http://127.0.0.1:8000</b> (Press CTRL+C to quit)
<font color="#4E9A06">INFO</font>:     Started reloader process [<font color="#34E2E2"><b>2265862</b></font>] using <font color="#34E2E2"><b>WatchFiles</b></font>

Ahora, ejecuta el comando `fastapi` con tu archivo:

<div class="termy">

```console
$ fastapi dev main.py

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

</div>

Y abre la documentación en <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

#### Sử dụng `Union` hay `Optional`

If you are using a Python version below 3.10, here's a tip from my very **subjective** point of view:

Nếu bạn đang sử dụng phiên bản Python dưới 3.10, đây là một mẹo từ ý kiến rất "chủ quan" của tôi:

* 🚨 Tránh sử dụng `Optional[SomeType]`
* Thay vào đó ✨ **sử dụng `Union[SomeType, None]`** ✨.

<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)
```

</div>

E abra a documentação em <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

<div class="termy">

```console
$ OPENAPI_URL= uvicorn main:app

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

</div>

⤴️ 🚥 👆 🚶 📛 `/openapi.json`, `/docs`, ⚖️ `/redoc` 👆 🔜 🤚 `404 Not Found` ❌ 💖:

```JSON
{
    "detail": "Not Found"
}