/// tip

Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="3"
{!> ../../docs_src/header_params/tutorial001.py!}
```

////

## Declare `Header` parameters

Then declare the header parameters using the same structure as with `Path`, `Query` and `Cookie`.

You can define the default value as well as all the extra validation or annotation parameters:

//// tab | Python 3.10+

###  ------------------------------- ###

declare -a residual_args
declare -a java_args
declare -a app_commands
declare -r real_script_path="$(realpath "$0")"
declare -r activator_home="$(realpath "$(dirname "$real_script_path")")"
declare -r app_version="1.3.2"

declare -r app_launcher="${activator_home}/activator-launch-${app_version}.jar"
declare -r script_name=activator
java_cmd=$(get_java_cmd)

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`. 🤓

///

## Header Parameters with a Pydantic Model

# Advanced Dependencies

## Parameterized dependencies

All the dependencies we have seen are a fixed function or class.

But there could be cases where you want to be able to set parameters on the dependency, without having to declare many different functions or classes.

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

/// tip

Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="3"
{!> ../../docs_src/cookie_params/tutorial001.py!}
```

////

## Declare `Cookie` parameters

Then declare the cookie parameters using the same structure as with `Path` and `Query`.

You can define the default value as well as all the extra validation or annotation parameters:

//// tab | Python 3.10+

It is used by Pydantic and FastAPI to explicitly declare that a value is required.

///

This will let **FastAPI** know that this parameter is required.

### Required, can be `None`

You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.

To do that, you can declare that `None` is a valid type but still use `...` as the default:

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

## Declare it as a parameter

To add it to your *path operation*, declare it the same way you declared path and query parameters:

{* ../../docs_src/body/tutorial001_py310.py hl[16] *}

...and declare its type as the model you created, `Item`.

## Results

With just that Python type declaration, **FastAPI** will:

## 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.

And you can also declare body parameters as optional, by setting the default to `None`:

//// tab | Python 3.10+

```Python hl_lines="18-20"
{!> ../../docs_src/body_multiple_params/tutorial001_an_py310.py!}
```

////

```

////

The files and form fields will be uploaded as form data and you will receive the files and form fields.

And you can declare some of the files as `bytes` and some as `UploadFile`.

/// warning

You can declare multiple `File` and `Form` parameters in a *path operation*, but you can't also declare `Body` fields that you expect to receive as JSON, as the request will have the body encoded using `multipart/form-data` instead of `application/json`.

With `Form` you can declare the same configurations as with `Body` (and `Query`, `Path`, `Cookie`), including validation, examples, an alias (e.g. `user-name` instead of `username`), etc.

/// info

`Form` is a class that inherits directly from `Body`.

///

/// tip