## Parâmetros opcionais

Da mesma forma, você pode declarar parâmetros de consulta opcionais, definindo o valor padrão para `None`:

=== "Python 3.10+"

    ```Python hl_lines="7"
    {!> ../../../docs_src/query_params/tutorial002_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params/tutorial002.py!}
    ```

```Python
from myapp import app
```

#### More details

Let's say your file is named `myapp.py`.

If you run it with:

<div class="termy">

```console
$ python myapp.py
```

</div>

then the internal variable `__name__` in your file, created automatically by Python, will have as value the string `"__main__"`.

So, the section:

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

=== "Python 3.10+"

    ```Python hl_lines="16  21"
    {!> ../../../docs_src/response_model/tutorial001_01_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="18  23"
    {!> ../../../docs_src/response_model/tutorial001_01_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="18  23"

=== "Python 3.9+"

    ```Python hl_lines="6  14  22"
    {!> ../../../docs_src/dependencies/tutorial008_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="5  13  21"
    {!> ../../../docs_src/dependencies/tutorial008_an.py!}
    ```

=== "Python 3.8+ nicht annotiert"

    !!! tip "Tipp"

=== "Python 3.10+"

    ```Python hl_lines="25"
    {!> ../../../docs_src/security/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="25"
    {!> ../../../docs_src/security/tutorial002_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="26"
    {!> ../../../docs_src/security/tutorial002_an.py!}
    ```

## Import `Field`

First, you have to import it:

=== "Python 3.10+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an.py!}
    ```

## 导入 `Field`

首先，从 Pydantic 中导入 `Field`：

=== "Python 3.10+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="4"
    {!> ../../../docs_src/body_fields/tutorial001_an.py!}
    ```

    {!> ../../../docs_src/dependencies/tutorial006.py!}
    ```

### 오류 발생시키기

다음 의존성은 기존 의존성과 동일하게 예외를 `raise`를 일으킬 수 있습니다:

=== "Python 3.9+"

    ```Python hl_lines="10  15"
    {!> ../../../docs_src/dependencies/tutorial006_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9  14"
    {!> ../../../docs_src/dependencies/tutorial006_an.py!}
    ```

    Z. B. `pip install python-multipart`.

## `Form` importieren

Importieren Sie `Form` von `fastapi`:

=== "Python 3.9+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/request_forms/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="1"

## `Header` importieren

Importieren Sie zuerst `Header`:

=== "Python 3.10+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/header_params/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/header_params/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/header_params/tutorial001_an.py!}