So, you can look for that specific exception inside the dependency with `except SomeException`.

In the same way, you can use `finally` to make sure the exit steps are executed, no matter if there was an exception or not.

{* ../../docs_src/dependencies/tutorial007.py hl[3,5] *}

## Sub-dependencies with `yield` { #sub-dependencies-with-yield }

It is possible to receive duplicate headers. That means, the same header with multiple values.

You can define those cases using a list in the type declaration.

You will receive all the values from the duplicate header as a Python `list`.

For example, to declare a header of `X-Token` that can appear more than once, you can write:

{* ../../docs_src/header_params/tutorial003_an_py310.py hl[9] *}

# Sub-dependencies { #sub-dependencies }

You can create dependencies that have **sub-dependencies**.

They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable" { #first-dependency-dependable }

You could create a first dependency ("dependable") like:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

     * Each tag configuration follows the pattern: tagname[attr=value].classname#id
     *
     * Examples:
     * - "div.content" matches div elements with class "content"
     * - "span#header" matches span elements with ID "header"
     * - "p[data-type=ad]" matches p elements with data-type attribute equal to "ad"
     *
     * @param value the comma-separated string of pruned tag configurations

folder using the session. The server side applications need not create a presigned URL and serve to the client for each file. Since, the client would have the session it can do it by itself.

The temporary security credentials returned by this API consists of an access key, a secret key, and a security token. Applications can use these temporary security credentials to sign calls to MinIO API operations. The policy applied to these temporary credentials is inherited from the MinIO user credentials....

reference "+f.id),g=a(f),i();else if("function"==typeof d.inlineErrorMessageCallback){if(g=d.inlineErrorMessageCallback(b,c,d),!g)return;i()}else{var j=this.getParentContainer(b);e=j.find("."+d.errorMessageClass+".help-block"),0===e.length&&(e=a("<span></span>").addClass("help-block").addClass(d.errorMessageClass),e.appendTo(j)),h(e)}},setMessageInTopOfForm:function(b,c,d,e){var f='<div class="{errorMessageClass} alert alert-danger"><strong>{errorTitle}</strong><ul>{fields}</ul></div>',g=!1;if("function"!=typeof...

You can use the same type declarations with `str`, `float`, `bool` and many other complex data types.

Several of these are explored in the next chapters of the tutorial.

## Order matters { #order-matters }

When creating *path operations*, you can find situations where you have a fixed path.

* Processing data:
    * For example, let's say you receive a file that must go through a slow process, you can return a response of "Accepted" (HTTP 202) and process the file in the background.

## Using `BackgroundTasks` { #using-backgroundtasks }

# `Request` class

You can declare a parameter in a *path operation function* or dependency to be of type `Request` and then you can access the raw request object directly, without any validation, etc.

You can import it directly from `fastapi`:

```python
from fastapi import Request
```

/// tip

    /**
     * Determines the address of a host given it's host name. The name can be a NetBIOS name like
     * "freto" or an IP address like "192.168.1.15". It cannot be a DNS name;
     * the analygous {@link jcifs.netbios.UniAddress} or {@link java.net.InetAddress}
     * <code>getByName</code> methods can be used for that.
     *
     * @param host
     *            hostname to resolve