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

	Owner             Owner    `xml:"Owner"`
	AccessControlList struct {
		Grants []grant `xml:"Grant"`
	} `xml:"AccessControlList"`
}

// PutBucketACLHandler - PUT Bucket ACL
// -----------------
// This operation uses the ACL subresource
// to set ACL for a bucket, this is a dummy call
// only responds success if the ACL is private.
func (api objectAPIHandlers) PutBucketACLHandler(w http.ResponseWriter, r *http.Request) {

	xhttp "github.com/minio/minio/internal/http"
)

var etagRegex = regexp.MustCompile("\"*?([^\"]*?)\"*?$")

// Validates the preconditions for CopyObjectPart, returns true if CopyObjectPart
// operation should not proceed. Preconditions supported are:
//
//	x-amz-copy-source-if-modified-since
//	x-amz-copy-source-if-unmodified-since
//	x-amz-copy-source-if-match
//	x-amz-copy-source-if-none-match

 */

package jcifs.smb1.dcerpc.msrpc;

import jcifs.smb1.smb1.FileEntry;
import jcifs.smb1.smb1.SmbShareInfo;

/**
 * MS-RPC share enumeration operation.
 *
 * This class implements the Server Service (SRVSVC) ShareEnumAll operation
 * for enumerating network shares on a remote server.
 */
public class MsrpcShareEnum extends srvsvc.ShareEnumAll {

    class MsrpcShareInfo1 extends SmbShareInfo {

```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

		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.

	// mainly set for certain WRITE operations.
	SkipDecommissioned bool
	// SkipRebalancing should be set to 'true' if the call should skip pools
	// participating in a rebalance operation. Typically set for 'write' operations.
	SkipRebalancing bool

	SrcPoolIdx int // set by PutObject/CompleteMultipart operations due to rebalance; used to prevent rebalance src, dst pools to be the same

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: