So, even with the code above that doesn't use Pydantic explicitly, FastAPI is using Pydantic to convert those standard dataclasses to Pydantic's own flavor of dataclasses.

And of course, it supports the same:

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

                                        },
                                    },
                                    "converted": {
                                        "summary": "An example with converted data",
                                        "description": "FastAPI can convert price `strings` to actual `numbers` automatically",
                                        "value": {"name": "Bar", "price": "35.4"},

## Convert any Data to JSON-compatible

To convert any data to JSON-compatible, read the docs for [Tutorial - JSON Compatible Encoder](../tutorial/encoder.md){.internal-link target=_blank}.

## OpenAPI Metadata - Docs

from typing import Annotated

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(
    strange_header: Annotated[str | None, Header(convert_underscores=False)] = None,
):

        deprecated: Union[deprecated, str, bool, None] = None,
        include_in_schema: bool = True,
        json_schema_extra: Union[Dict[str, Any], None] = None,
        **extra: Any,
    ):
        self.convert_underscores = convert_underscores
        super().__init__(
            default=default,
            default_factory=default_factory,
            annotation=annotation,
            alias=alias,

따라서, `User_Agent` 등과 같이 첫 문자를 대문자화할 필요없이 파이썬 코드에서처럼 `user_agent`로 사용합니다.

만약 언더스코어를 하이픈으로 자동 변환을 비활성화해야 할 어떤 이유가 있다면, `Header`의 `convert_underscores` 매개변수를 `False`로 설정하십시오:

```Python hl_lines="10"
{!../../../docs_src/header_params/tutorial002.py!}
```

!!! warning "경고"
    `convert_underscore`를 `False`로 설정하기 전에, 어떤 HTTP 프록시들과 서버들은 언더스코어가 포함된 헤더 사용을 허락하지 않는다는 것을 명심하십시오.

## 중복 헤더

            fields will be ignored at serialization time.
            """
        ),
    ] = None,
    convert_underscores: Annotated[
        bool,
        Doc(
            """
            Automatically convert underscores to hyphens in the parameter field name.

            Read more about it in the

Если по какой-либо причине вам необходимо отключить автоматическое преобразование подчеркиваний в дефисы, установите для параметра `convert_underscores` в `Header` значение `False`:

=== "Python 3.10+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/header_params/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

因此，默认情况下，`Header` 把参数名中的字符由下划线（`_`）改为连字符（`-`）来提取并存档请求头 。

同时，HTTP 的请求头不区分大小写，可以使用 Python 标准样式（即 **snake_case**）进行声明。

因此，可以像在 Python 代码中一样使用 `user_agent` ，无需把首字母大写为 `User_Agent` 等形式。

如需禁用下划线自动转换为连字符，可以把 `Header` 的 `convert_underscores` 参数设置为 `False`：

=== "Python 3.10+"

    ```Python hl_lines="10"
    {!> ../../../docs_src/header_params/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

FastAPI will use this `response_model` to do all the data documentation, validation, etc. and also to **convert and filter the output data** to its type declaration.

!!! tip
    If you have strict type checks in your editor, mypy, etc, you can declare the function return type as `Any`.