<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

    end
```

/// tip

It's very common in Python packages to try the best to **avoid breaking changes** in **new versions**, but it's better to be safe, and install newer versions intentionally and when you can run the tests to check everything is working correctly.

///

	bp.Put(make([]byte, bp.w, bp.wcap-1)) // wrong capacity is rejected (less)
	bp.Put(make([]byte, bp.w, bp.wcap+1)) // wrong capacity is rejected (more)
	bp.Put(make([]byte, width))           // wrong capacity is rejected (very less)
	if len(bp.c) > 0 {
		t.Fatal("bytepool should have rejected invalid packets")
	}

	// Try putting a short slice into pool
	bp.Put(make([]byte, bp.w, bp.wcap)[:2])
	if len(bp.c) != 1 {

///

## Returning a custom `Response` { #returning-a-custom-response }

The example above shows all the parts you need, but it's not very useful yet, as you could have just returned the `item` directly, and **FastAPI** would put it in a `JSONResponse` for you, converting it to a `dict`, etc. All that by default.

Containers (mainly Linux containers) are a very **lightweight** way to package applications including all their dependencies and necessary files while keeping them isolated from other containers (other applications or components) in the same system.

	if err != nil {
		return err
	}
	x.ClientConversation = x.NewConversation()
	return nil
}

// Step takes a string provided from a server (or just an empty string for the
// very first conversation step) and attempts to move the authentication
// conversation forward.  It returns a string to be sent to the server or an
// error if the server message is invalid.  Calling Step after a conversation

                    }
                }
            }
        } catch (IOException | XMLStreamException e) {
            // The root locator can be used very early during the setup of Maven,
            // even before the arguments from the command line are parsed.  Any exception
            // that would happen here should cause the build to fail at a later stage

<div class="screenshot">
<img src="/img/tutorial/query-param-models/image01.png">
</div>

## Forbid Extra Query Parameters { #forbid-extra-query-parameters }

In some special use cases (probably not very common), you might want to **restrict** the query parameters that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

          '\n', "<newline>",
          '\t', "<tab>",
          '&', "<and>");
  private static final char[] NO_CHARS = new char[0];

  public void testReplacements() throws IOException {
    // In reality this is not a very sensible escaper to have (if you are only
    // escaping elements from a map you would use a ArrayBasedCharEscaper).
    UnicodeEscaper escaper =
        new ArrayBasedUnicodeEscaper(

///

## Forbid Extra Cookies { #forbid-extra-cookies }

In some special use cases (probably not very common), you might want to **restrict** the cookies that you want to receive.