Como ejemplo, tomemos esta función:

{* ../../docs_src/python_types/tutorial009c_py39.py hl[1,4] *}

El parámetro `name` está definido como `Optional[str]`, pero **no es opcional**, no puedes llamar a la función sin el parámetro:

```Python
say_hi()  # ¡Oh, no, esto lanza un error! 😱
```

El parámetro `name` sigue siendo **requerido** (no *opcional*) porque no tiene un valor predeterminado. Aún así, `name` acepta `None` como valor:

///

## Corpo da requisição + parâmetros de rota { #request-body-path-parameters }

Você pode declarar parâmetros de rota e corpo da requisição ao mesmo tempo.

O **FastAPI** irá reconhecer que os parâmetros da função que combinam com parâmetros de rota devem ser **retirados da rota**, e que parâmetros da função que são declarados como modelos Pydantic sejam **retirados do corpo da requisição**.

# Body - Multiple Parameters { #body-multiple-parameters }

Now that we have seen how to use `Path` and `Query`, let's see more advanced uses of request body declarations.

## Mix `Path`, `Query` and body parameters { #mix-path-query-and-body-parameters }

First, of course, you can mix `Path`, `Query` and request body parameter declarations freely and **FastAPI** will know what to do.

    /**
     * Add the created action message for the key 'constraints.Size.message' with parameters.
     * <pre>
     * message: The size of {item} must be between {min} and {max}.
     * </pre>
     * @param property The property name for the message. (NotNull)
     * @param min The parameter min for message. (NotNull)
     * @param max The parameter max for message. (NotNull)
     * @return this. (NotNull)
     */

# Headers de Response { #response-headers }

## Usa un parámetro `Response` { #use-a-response-parameter }

Puedes declarar un parámetro de tipo `Response` en tu *path operation function* (como puedes hacer para cookies).

Y luego puedes establecer headers en ese objeto de response *temporal*.

{* ../../docs_src/response_headers/tutorial002_py39.py hl[1, 7:8] *}

# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

    public void setParameters(List<Parameter> parameters) throws DuplicateParameterException {
        this.parameters.clear();
        for (Parameter parameter : parameters) {
            addParameter(parameter);
        }
    }

    /**
     * @param parameter add a new parameter
     * @throws DuplicateParameterException if any
     */
    public void addParameter(Parameter parameter) throws DuplicateParameterException {

    }

    /**
     * Extracts and parses parameters from the request query string.
     * Applies the specified character encoding to decode parameter values.
     *
     * @param request the HTTP request containing the query string
     * @param enc the character encoding to use for decoding
     * @return a map of parameter names to their decoded values

import java.util.Arrays;

/**
 * Entity class representing a request parameter with a name and associated values.
 * This class encapsulates HTTP request parameters that can have multiple values,
 * such as query parameters, form parameters, or other request-related data.
 *
 * <p>This class is immutable and thread-safe. Once created, the parameter name
 * and values cannot be modified.</p>
 *
 */
public class RequestParameter {

{* ../../docs_src/body/tutorial002_py310.py *}

## Request body + path parameters { #request-body-path-parameters }

You can declare path parameters and request body at the same time.

**FastAPI** will recognize that the function parameters that match path parameters should be **taken from the path**, and that function parameters that are declared to be Pydantic models should be **taken from the request body**.