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_py39.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

```mermaid
sequenceDiagram

participant client as Client
participant handler as Exception handler
participant dep as Dep with yield
participant operation as Path Operation
participant tasks as Background tasks

    Note over client,operation: Can raise exceptions, including HTTPException
    client ->> dep: Start request
    Note over dep: Run code up to yield
    opt raise Exception

# Body - Campos { #body-fields }

De la misma manera que puedes declarar validaciones adicionales y metadatos en los parámetros de las *path operation function* con `Query`, `Path` y `Body`, puedes declarar validaciones y metadatos dentro de los modelos de Pydantic usando `Field` de Pydantic.

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

Primero, tienes que importarlo:

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

/// warning | Advertencia

///

This parameter doesn't create that endpoint / *path operation*, but declares that the URL `/token` will be the one that the client should use to get the token. That information is used in OpenAPI, and then in the interactive API documentation systems.

We will soon also create the actual path operation.

/// info

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.

        // Wait for reset timeout
        Thread.sleep(1100);

        // Execute successful operation - should transition to HALF_OPEN then potentially CLOSED
        String result = circuitBreaker.executeWithCircuitBreaker(() -> "success");
        assertEquals("success", result, "Operation should succeed");
        assertEquals(State.HALF_OPEN, circuitBreaker.getState(), "Circuit should be in HALF_OPEN");

    /**
     * Creates a new CreateForm instance.
     */
    public CreateForm() {
        // Default constructor
    }

    /**
     * The CRUD operation mode for this form.
     * Indicates whether this is a create, read, update, or delete operation.
     */
    @ValidateTypeFailure
    public Integer crudMode;

    /**
     * The name of the access token.

which in turn are made up of memory operations.
</p>

<p>
A <i>memory operation</i> is modeled by four details:
</p>
<ul>
	<li>its kind, indicating whether it is an ordinary data read, an ordinary data write,
    or a <i>synchronizing operation</i> such as an atomic data access,
	a mutex operation, or a channel operation,</li>
	<li>its location in the program,</li>

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`:

        initCause(readFailure)
      }
    }
  }

  abstract val path: Any

  /**
   * Reads the public suffix list treating the operation as uninterruptible. We always want to read
   * the list otherwise we'll be left in a bad state. If the thread was interrupted prior to this
   * operation, it will be re-interrupted after the list is read.
   */
  private fun readTheListUninterruptibly() {
    var interrupted = false
    try {