You declare the "shape" of the data as classes with attributes.

And each attribute has a type.

Then you create an instance of that class with some values and it will validate the values, convert them to the appropriate type (if that's the case) and give you an object with all the data.

And you get all the editor support with that resulting object.

An example from the official Pydantic docs:

    Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.
    As these keys may not necessarily be part of the OpenAPI specification, some OpenAPI tools, for example [the OpenAPI validator](https://validator.swagger.io/), may not work with your generated schema.

## Recap

You can use Pydantic's `Field` to declare extra validations and metadata for model attributes.

    field_info = FieldInfo(annotation=str)
    field = ModelField(name="foo", field_info=field_info)
    assert field.default is Undefined


@needs_pydanticv1
def test_upload_file_dummy_with_info_plain_validator_function():
    # For coverage
    assert UploadFile.__get_pydantic_core_schema__(str, lambda x: None) == {}


@needs_pydanticv1
def test_union_scalar_list():
    # For coverage

## Opcjonalne zależności

Używane przez Pydantic:

* <a href="https://github.com/JoshData/python-email-validator" target="_blank"><code>email_validator</code></a> - dla walidacji adresów email.

Używane przez Starlette:

* <a href="https://www.python-httpx.org" target="_blank"><code>httpx</code></a> - Wymagane jeżeli chcesz korzystać z `TestClient`.

## Необязательные зависимости

Используется Pydantic:

* <a href="https://github.com/JoshData/python-email-validator" target="_blank"><code>email_validator</code></a> - для проверки электронной почты.

Используется Starlette:

## Dipendenze opzionali

Usate da Pydantic:

* <a href="https://github.com/JoshData/python-email-validator" target="_blank"><code>email_validator</code></a> - per la validazione di email.

Usate da Starlette:

* <a href="http://docs.python-requests.org" target="_blank"><code>requests</code></a> - Richiesto se vuoi usare il `TestClient`.

想了解更多，请查阅 <a href="https://fastapi.tiangolo.com/zh/benchmarks/" class="internal-link" target="_blank">基准测试</a> 章节。

## 可选依赖

用于 Pydantic：

* <a href="https://github.com/JoshData/python-email-validator" target="_blank"><code>email_validator</code></a> - 用于 email 校验。

用于 Starlette：

* <a href="https://www.python-httpx.org" target="_blank"><code>httpx</code></a> - 使用 `TestClient` 时安装。

Imaginez que vous vouliez que votre paramètre se nomme `item-query`.

Comme dans la requête :

```
http://127.0.0.1:8000/items/?item-query=foobaritems
```

Mais `item-query` n'est pas un nom de variable valide en Python.

Le nom le plus proche serait `item_query`.

Mais vous avez vraiment envie que ce soit exactement `item-query`...

# TODO: remove when deprecating Pydantic v1
def test_upload_file_invalid():
    with pytest.raises(ValueError):
        UploadFile.validate("not a Starlette UploadFile")


def test_upload_file_invalid_pydantic_v2():
    with pytest.raises(ValueError):
        UploadFile._validate("not a Starlette UploadFile", {})


def test_default_placeholder_equals():
    placeholder_1 = Default("a")
    placeholder_2 = Default("a")

# Body - Nested Models

With **FastAPI**, you can define, validate, document, and use arbitrarily deeply nested models (thanks to Pydantic).

## List fields

You can define an attribute to be a subtype. For example, a Python `list`:

=== "Python 3.10+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/body_nested_models/tutorial001_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="14"