## Development

By the time I started creating **FastAPI** itself, most of the pieces were already in place, the design was defined, the requirements and tools were ready, and the knowledge about the standards and specifications was clear and fresh.

## Future

By this point, it's already clear that **FastAPI** with its ideas is being useful for many people.

    You can use a closing code from the <a href="https://tools.ietf.org/html/rfc6455#section-7.4.1" class="external-link" target="_blank">valid codes defined in the specification</a>.

### Try the WebSockets with dependencies

If your file is named `main.py`, run your application with:

<div class="termy">

```console
$ fastapi dev main.py

    ```

## `Union` or `anyOf`

You can declare a response to be the `Union` of two types, that means, that the response would be any of the two.

It will be defined in OpenAPI with `anyOf`.

To do that, use the standard Python type hint <a href="https://docs.python.org/3/library/typing.html#typing.Union" class="external-link" target="_blank">`typing.Union`</a>:

!!! note

    return burgers
```

### More technical details

You might have noticed that `await` can only be used inside of functions defined with `async def`.

But at the same time, functions defined with `async def` have to be "awaited". So, functions with `async def` can only be called inside of functions defined with `async def` too.

So, about the egg and the chicken, how do you call the first `async` function?

                    corresponding JSON.
                * Filtering: the JSON sent to the client will only contain the data
                    (fields) defined in the `response_model`. If you returned an object
                    that contains an attribute `password` but the `response_model` does
                    not include that field, the JSON sent to the client would not have

`async def`f 함수를 호출하고자 할 때, "대기"해야합니다. 따라서, 아래는 동작하지 않습니다.

```Python
# This won't work, because get_burgers was defined with: async def
burgers = get_burgers(2)
```

---

따라서, `await`f를 사용해서 호출할 수 있는 라이브러리를 사용한다면, 다음과 같이 `async def`를 사용하는 *경로 작동 함수*를 생성해야 합니다:

```Python hl_lines="2-3"
@app.get('/burgers')

So, a Python class is also a **callable**.

Then, in **FastAPI**, you could use a Python class as a dependency.

What FastAPI actually checks is that it is a "callable" (function, class or anything else) and the parameters defined.

If you pass a "callable" as a dependency in **FastAPI**, it will analyze the parameters for that "callable", and process them in the same way as the parameters for a *path operation function*. Including sub-dependencies.

🕐❔ 👆 💚 🤙 `async def` 🔢, 👆 ✔️ "⌛" ⚫️. , 👉 🏆 🚫 👷:

```Python
# This won't work, because get_burgers was defined with: async def
burgers = get_burgers(2)
```

---

, 🚥 👆 ⚙️ 🗃 👈 💬 👆 👈 👆 💪 🤙 ⚫️ ⏮️ `await`, 👆 💪 ✍ *➡ 🛠️ 🔢* 👈 ⚙️ ⚫️ ⏮️ `async def`, 💖:

```Python hl_lines="2-3"
@app.get('/burgers')

        * `password`: some next chapters will cover examples of this.
* `openIdConnect`: has a way to define how to discover OAuth2 authentication data automatically.
    * This automatic discovery is what is defined in the OpenID Connect specification.


!!! tip
    Integrating other authentication/authorization providers like Google, Facebook, Twitter, GitHub, etc. is also possible and relatively easy.

    """

    def __init__(
        self,
        code: Annotated[
            int,
            Doc(
                """
                A closing code from the
                [valid codes defined in the specification](https://datatracker.ietf.org/doc/html/rfc6455#section-7.4.1).
                """
            ),
        ],
        reason: Annotated[
            Union[str, None],
            Doc(