<img src="/img/python-types/image06.png">

Notice that this means "`one_person` is an **instance** of the class `Person`".

It doesn't mean "`one_person` is the **class** called `Person`".

## Pydantic models

<a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> is a Python library to perform data validation.

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

///

`RequestValidationError` ist eine Unterklasse von Pydantics <a href="https://pydantic-docs.helpmanual.io/usage/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a>.

**FastAPI** verwendet diesen, sodass Sie, wenn Sie ein Pydantic-Modell für `response_model` verwenden, und ihre Daten fehlerhaft sind, einen Fehler in ihrem Log sehen.

    * Convert Python types (`str`, `int`, `float`, `bool`, `list`, etc).
    * `datetime` objects.
    * `UUID` objects.
    * Database models.
    * ...and many more.
* Automatic interactive API documentation, including 2 alternative user interfaces:
    * Swagger UI.
    * ReDoc.

---

Coming back to the previous code example, **FastAPI** will:

* etc.

In these cases, you would normally return an **HTTP status code** in the range of **400** (from 400 to 499).

This is similar to the 200 HTTP status codes (from 200 to 299). Those "200" status codes mean that somehow there was a "success" in the request.

The status codes in the 400 range mean that there was an error from the client.

Remember all those **"404 Not Found"** errors (and jokes)?

## Use `HTTPException`

/// tip | "Tipp"

Pydantic verhält sich speziell, wenn Sie `Optional` oder `Union[Etwas, None]` ohne einen Default-Wert verwenden. Sie können darüber in der Pydantic Dokumentation unter <a href="https://docs.pydantic.dev/2.3/usage/models/#required-fields" class="external-link" target="_blank">Required fields</a> mehr erfahren.

///

## Typhinweise mit Metadaten-Annotationen

import warnings
from enum import Enum
from typing import Any, Callable, Dict, List, Optional, Sequence, Union

from fastapi.openapi.models import Example
from pydantic.fields import FieldInfo
from typing_extensions import Annotated, deprecated

from ._compat import PYDANTIC_V2, PYDANTIC_VERSION, Undefined

_Unset: Any = Undefined


class ParamTypes(Enum):
    query = "query"
    header = "header"
    path = "path"

<img src="/img/python-types/image06.png">

Lưu ý rằng, điều này có nghĩa rằng "`one_person`" là một **thực thể** của lớp `Person`.

Nó không có nghĩa "`one_person`" là một **lớp** gọi là `Person`.

## Pydantic models

<a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a> là một thư viện Python để validate dữ liệu hiệu năng cao.

### `RequestValidationError` vs `ValidationError`

/// warning | "警告"

如果您觉得现在还用不到以下技术细节，可以先跳过下面的内容。

///

`RequestValidationError` 是 Pydantic 的 <a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a> 的子类。

**FastAPI** 调用的就是 `RequestValidationError` 类，因此，如果在 `response_model` 中使用 Pydantic 模型，且数据有错误时，在日志中就会看到这个错误。

import org.apache.maven.api.model.Repository;
import org.apache.maven.api.model.Resource;
import org.apache.maven.model.Model;
import org.apache.maven.model.building.ModelBuildingRequest;
import org.apache.maven.model.building.ModelProblem.Severity;
import org.apache.maven.model.building.ModelProblem.Version;
import org.apache.maven.model.building.ModelProblemCollector;
import org.apache.maven.model.building.ModelProblemCollectorRequest;

    full_name = user_dict["full_name"],
    disabled = user_dict["disabled"],
    hashed_password = user_dict["hashed_password"],
)
```

/// info | "说明"

`user_dict` 的说明，详见[**更多模型**一章](../extra-models.md#user_indict){.internal-link target=_blank}。

///

## 返回 Token

`token` 端点的响应必须是 JSON 对象。

响应返回的内容应该包含 `token_type`。本例中用的是**Bearer**Token，因此， Token 类型应为**`bearer`**。