The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

# Header Parameters

You can define Header parameters the same way you define `Query`, `Path` and `Cookie` parameters.

## Import `Header`

First import `Header`:

//// tab | Python 3.10+

```Python hl_lines="3"
{!> ../../docs_src/header_params/tutorial001_an_py310.py!}
```

////

//// tab | Python 3.9+

```Python hl_lines="3"
{!> ../../docs_src/header_params/tutorial001_an_py39.py!}
```

////

# to reference the most recent versions of the SIG Build Docker images.
name: Update RBE Configs
on:
  workflow_dispatch:

permissions:
  contents: read

jobs:
  rbe:
    name: Update RBE Configs
    runs-on: ubuntu-latest
    if: github.repository == 'tensorflow/tensorflow' # Don't do this in forks
    steps:
    - name: Checkout code
      uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2

///

```Python hl_lines="7  13"
{!> ../../docs_src/request_files/tutorial001_03.py!}
```

////

## Multiple File Uploads

It's possible to upload several files at the same time.

They would be associated to the same "form field" sent using "form data".

To use that, declare a list of `bytes` or `UploadFile`:

//// tab | Python 3.9+

```Python hl_lines="10  15"

They are just a convenience, they hold the same number, but that way you can use the editor's autocomplete to find them:

<img src="/img/tutorial/response-status-code/image02.png">

/// note | "Technical Details"

You could also use `from starlette import status`.

 *     their equivalent on the result of {@code Traverser.forTree(tree)} where {@code tree}
 *     implements {@code SuccessorsFunction}, which has a similar API as {@link #children} or can be
 *     the same lambda function as passed into {@link #using(Function)}.
 *     <p>This class is scheduled to be removed in October 2019.
 */
// TODO(b/68134636): Remove by 2019-10
@Deprecated
@Beta
@GwtCompatible

	"github.com/secure-io/sio-go"
	"github.com/secure-io/sio-go/sioutil"
)

// EncryptBytes encrypts the plaintext with a key managed by KMS.
// The context is bound to the returned ciphertext.
//
// The same context must be provided when decrypting the
// ciphertext.
func EncryptBytes(k *kms.KMS, plaintext []byte, context kms.Context) ([]byte, error) {
	ciphertext, err := Encrypt(k, bytes.NewReader(plaintext), context)

// Type is here for the purposes of documentation only. It is a stand-in
// for any Go type, but represents the same type for any given function
// invocation.
type Type int

// Type1 is here for the purposes of documentation only. It is a stand-in
// for any Go type, but represents the same type for any given function
// invocation.
type Type1 int

For example, if you have a function:

```Python
@lru_cache
def say_hi(name: str, salutation: str = "Ms."):
    return f"Hello {salutation} {name}"
```

your program could execute like this:

```mermaid
sequenceDiagram

participant code as Code

  }

  // Node/edge sets are the same, but node/edge connections differ due to edge type.
  @Test
  public void equivalent_directedVsUndirected() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(oppositeType(edgeType));
    g2.putEdge(N1, N2);

    assertThat(graph).isNotEqualTo(g2);
  }

  // Node/edge sets and node/edge connections are the same, but directedness differs.
  @Test