Let's imagine you want to get the client's IP address/host inside of your *path operation function*.

For that you need to access the request directly.

{* ../../docs_src/using_request_directly/tutorial001.py hl[1,7:8] *}

By declaring a *path operation function* parameter with the type being the `Request` **FastAPI** will know to pass the `Request` in that parameter.

/// tip

En este caso, este `__call__` es lo que **FastAPI** usará para comprobar parámetros adicionales y sub-dependencias, y es lo que llamará para pasar un valor al parámetro en tu *path operation function* más adelante.

## Parametrizar la instance

Y ahora, podemos usar `__init__` para declarar los parámetros de la instance que podemos usar para "parametrizar" la dependencia:

# Body - Fields { #body-fields }

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field` { #import-field }

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

    return values().contains(value);
  }

  /**
   * Guaranteed to throw an exception and leave the table unmodified.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  public final void clear() {
    throw new UnsupportedOperationException();
  }

  /**

Estos `examples` específicos de **OpenAPI** van en otra sección en la especificación de OpenAPI. Van en los **detalles para cada *path operation***, no dentro de cada JSON Schema.

Y Swagger UI ha soportado este campo particular de `examples` por un tiempo. Así que, puedes usarlo para **mostrar** diferentes **ejemplos en la interfaz de documentación**.

		return "Unknown"
	}
}

// InsufficientReadQuorum storage cannot satisfy quorum for read operation.
type InsufficientReadQuorum struct {
	Bucket string
	Object string
	Err    error
	Type   RQErrType
}

func (e InsufficientReadQuorum) Error() string {
	return "Storage resources are insufficient for the read operation " + e.Bucket + "/" + e.Object
}

// Unwrap the error.

Si pasas un "callable" como dependencia en **FastAPI**, analizará los parámetros de ese "callable", y los procesará de la misma manera que los parámetros de una *path operation function*. Incluyendo sub-dependencias.

Eso también se aplica a los callables sin parámetros. Igual que sería para *path operation functions* sin parámetros.

Entonces, podemos cambiar la dependencia "dependable" `common_parameters` de arriba a la clase `CommonQueryParams`:

In this case, this `__call__` is what **FastAPI** will use to check for additional parameters and sub-dependencies, and this is what will be called to pass a value to the parameter in your *path operation function* later.

## Parameterize the instance { #parameterize-the-instance }

And now, we can use `__init__` to declare the parameters of the instance that we can use to "parameterize" the dependency:

 */

package com.google.common.primitives;

import com.google.common.annotations.GwtCompatible;

@GwtCompatible
final class TestPlatform {
  static int reduceIterationsIfGwt(int iterations) {
    return iterations / 10;
  }

  private TestPlatform() {}

Because it's a Python exception, you don't `return` it, you `raise` it.

This also means that if you are inside a utility function that you are calling inside of your *path operation function*, and you raise the `HTTPException` from inside of that utility function, it won't run the rest of the code in the *path operation function*, it will terminate that request right away and send the HTTP error from the `HTTPException` to the client.