the dependency is declared again for the rest of the request (for example
            if the dependency is needed by several dependencies), the value will be
            re-used for the rest of the request.

            Set `use_cache` to `False` to disable this behavior and ensure the
            dependency is called again (if declared more than once) in the same request.
            """

# Usando Dataclasses { #using-dataclasses }

FastAPI é construído em cima do **Pydantic**, e eu tenho mostrado como usar modelos Pydantic para declarar requisições e respostas.

Mas o FastAPI também suporta o uso de <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> da mesma forma:

{* ../../docs_src/dataclasses_/tutorial001_py310.py hl[1,6:11,18:19] *}

# Usando Dataclasses { #using-dataclasses }

FastAPI está construido sobre **Pydantic**, y te he estado mostrando cómo usar modelos de Pydantic para declarar requests y responses.

Pero FastAPI también soporta el uso de <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> de la misma manera:

{* ../../docs_src/dataclasses_/tutorial001_py310.py hl[1,6:11,18:19] *}

    * If it is not, the client will see a useful, clear error.
* Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests.
    * As the `q` parameter is declared with `= None`, it is optional.
    * Without the `None` it would be required (as is the body in the case with `PUT`).
* For `PUT` requests to `/items/{item_id}`, read the body as JSON:

class FastAPIError(RuntimeError):
    """
    A generic, FastAPI-specific error.
    """


class DependencyScopeError(FastAPIError):
    """
    A dependency declared that it depends on another dependency with an invalid
    (narrower) scope.
    """


class ValidationException(Exception):
    def __init__(
        self,
        errors: Sequence[Any],
        *,

Zum Beispiel würde `list[int]` überprüfen (und dokumentieren), dass der Inhalt der Liste Ganzzahlen sind. Aber `list` alleine würde das nicht.

///

## Mehr Metadaten deklarieren { #declare-more-metadata }

Sie können mehr Informationen über den Parameter hinzufügen.

Diese Informationen werden in das generierte OpenAPI aufgenommen und von den Dokumentationsoberflächen und externen Tools verwendet.

    * If it is not, the client will see a useful, clear error.
* Check if there is an optional query parameter named `q` (as in `http://127.0.0.1:8000/items/foo?q=somequery`) for `GET` requests.
    * As the `q` parameter is declared with `= None`, it is optional.
    * Without the `None` it would be required (as is the body in the case with `PUT`).
* For `PUT` requests to `/items/{item_id}`, read the body as JSON:

    * This is useful while calling external services, performing costly computation, etc.
    * This also means that if a dependency was declared as a *path operation decorator* dependency, possibly at the router level (with `.include_router()`) and then it is declared again in a specific *path operation*, the dependency will be called only once.