<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.

/// info

Beachten Sie, dass der `TestClient` Daten empfängt, die nach JSON konvertiert werden können, keine Pydantic-Modelle.

    * 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:

### Memória por Processo

Agora, quando o programa carrega coisas na memória, por exemplo, um modelo de aprendizado de máquina em uma variável, ou o conteúdo de um arquivo grande em uma variável, tudo isso **consome um pouco da memória (RAM)** do servidor.

</p>

<h2 id="model">Memory Model</h2>

<p>
The following formal definition of Go's memory model closely follows
the approach presented by Hans-J. Boehm and Sarita V. Adve in
“<a href="https://www.hpl.hp.com/techreports/2008/HPL-2008-56.pdf">Foundations of the C++ Concurrency Memory Model</a>”,
published in PLDI 2008.

Adotar temporariamente esse ponto de vista (do *desenvolvedor externo*) pode ajudar a sentir que é mais óbvio onde colocar os parâmetros, o modelo Pydantic para o corpo, para a resposta, etc. para essa *API externa*.

///

### Criar um `APIRouter` para o callback

Primeiramente crie um novo `APIRouter` que conterá um ou mais callbacks.

///

`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.

///

`RequestValidationError` is a sub-class of Pydantic's <a href="https://docs.pydantic.dev/latest/concepts/models/#error-handling" class="external-link" target="_blank">`ValidationError`</a>.

**FastAPI** uses it so that, if you use a Pydantic model in `response_model`, and your data has an error, you will see the error in your log.

/// 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"