And of course, it supports the same:

* data validation
* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

!!! info
    Keep in mind that dataclasses can't do everything Pydantic models can do.

    * A "token" is just a string with some content that we can use later to verify this user.
    * Normally, a token is set to expire after some time.
        * So, the user will have to log in again at some point later.
        * And if the token is stolen, the risk is less. It is not like a permanent key that will work forever (in most of the cases).

### Certificate Renewal

At some point in the future, each certificate would **expire** (about 3 months after acquiring it).

And then, there would be another program (in some cases it's another program, in some cases it could be the same TLS Termination Proxy) that would talk to Let's Encrypt, and renew the certificate(s).

    with pytest.raises(WebSocketDisconnect):
        with client.websocket_connect("/items/bar/ws?token=some-token") as websocket:
            message = "Message one"
            websocket.send_text(message)
            data = websocket.receive_text()
            assert data == "Session cookie or query token value is: some-token"
            data = websocket.receive_text()

```Python
    uvicorn.run(app, host="0.0.0.0", port=8000)
```

이 실행됩니다.

---

해당 모듈(파일)을 가져오면 이런 일이 발생하지 않습니다

그래서 다음과 같은 다른 파일 `importer.py`가 있는 경우:

```Python
from myapp import app

# Some more code
```

이 경우 `myapp.py` 내부의 자동 변수에는 값이 `"__main__"`인 변수 `__name__`이 없습니다.

따라서 다음 행

```Python
    uvicorn.run(app, host="0.0.0.0", port=8000)
```

은 실행되지 않습니다.

!!! info "정보"

```

### Testing file

Then you could have a file `test_main.py` with your tests. It could live on the same Python package (the same directory with a `__init__.py` file):

``` hl_lines="5"
.
├── app
│   ├── __init__.py
│   ├── main.py
│   └── test_main.py
```

Because this file is in the same package, you can use relative imports to import the object `app` from the `main` module (`main.py`):

```Python hl_lines="3"

Так, если у вас есть объект `something` (который может _не_ быть функцией) и вы можете "вызвать" его (выполнить) как:

```Python
something()
```

или

```Python
something(some_argument, some_keyword_argument="foo")
```

в таком случае он является "вызываемым".

## Классы как зависимости

Вы можете заметить, что для создания экземпляра класса в Python используется тот же синтаксис.

Например:

```Python hl_lines="6"
{!../../../docs_src/path_params/tutorial004.py!}
```

!!! tip
    You could need the parameter to contain `/home/johndoe/myfile.txt`, with a leading slash (`/`).

    In that case, the URL would be: `/files//home/johndoe/myfile.txt`, with a double slash (`//`) between `files` and `home`.

## Recap

With **FastAPI**, by using short, intuitive and standard Python type declarations, you get:

    {!> ../../../docs_src/request_forms_and_files/tutorial001.py!}
    ```

The files and form fields will be uploaded as form data and you will receive the files and form fields.

And you can declare some of the files as `bytes` and some as `UploadFile`.

!!! warning

But you are not restricted to using some specific data model, class or type.

Do you want to have an `id` and `email` and not have any `username` in your model? Sure. You can use these same tools.

Do you want to just have a `str`? Or just a `dict`? Or a database class model instance directly? It all works the same way.