```json
{
    "description": "Some data",
    "data": "aGVsbG8="
}
```

/// tip

`aGVsbG8=` is the base64 encoding of `hello`.

///

And then Pydantic will decode the base64 string and give you the original bytes in the `data` field of the model.

You will receive a response like:

```json
{
  "description": "Some data",
  "content": "hello"
}
```

# Configure Swagger UI { #configure-swagger-ui }

You can configure some extra [Swagger UI parameters](https://swagger.io/docs/open-source-tools/swagger-ui/usage/configuration/).

To configure them, pass the `swagger_ui_parameters` argument when creating the `FastAPI()` app object or to the `get_swagger_ui_html()` function.

`swagger_ui_parameters` receives a dictionary with the configurations passed to Swagger UI directly.

/// tip

**GraphQL** solves some very specific use cases.

It has **advantages** and **disadvantages** when compared to common **web APIs**.

Make sure you evaluate if the **benefits** for your use case compensate the **drawbacks**. 🤓

///

## GraphQL Libraries { #graphql-libraries }

* Great editor support.
* Data conversion from incoming requests.
* Data conversion for response data.
* Data validation.
* Automatic annotation and documentation.

## Other data types { #other-data-types }

Here are some of the additional data types you can use:

* `UUID`:
    * A standard "Universally Unique Identifier", common as an ID in many databases and systems.
    * In requests and responses will be represented as a `str`.

                "price": 50.5,
                "description": "Some Foo",
                "tax": 0.1,
            },
        },
    )
    assert response.status_code == 200
    assert response.json() == {
        "item_id": 5,
        "item": {
            "name": "Foo",
            "price": 50.5,
            "description": "Some Foo",
            "tax": 0.1,
        },
    }

If for some reason you need to disable automatic conversion of underscores to hyphens, set the parameter `convert_underscores` of `Header` to `False`:

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

/// warning

Before setting `convert_underscores` to `False`, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.

///

# Advanced Python Types { #advanced-python-types }

Here are some additional ideas that might be useful when working with Python types.

## Using `Union` or `Optional` { #using-union-or-optional }

If your code for some reason can't use `|`, for example if it's not in a type annotation but in something like `response_model=`, instead of using the vertical bar (`|`) you can use `Union` from `typing`.

      for (Object o : elements) {
        Entry<?, ?> entry = (Entry<?, ?>) o;
        // These come from Entry<K, Collection<V>>> objects somewhere.
        @SuppressWarnings("unchecked")
        K key = (K) entry.getKey();
        keySet.add(key);
        for (Object v : (Collection<?>) entry.getValue()) {
          // These come from Entry<K, Collection<V>>> objects somewhere.
          @SuppressWarnings("unchecked")

    * This is particularly important for **security**, we'll see more of that below.

## `response_model` Parameter { #response-model-parameter }

There are some cases where you need or want to return some data that is not exactly what the type declares.

        assertDoesNotThrow(() -> bufferManager.cleanup());

        // After cleanup, all regions should be released (but the count may not match exactly
        // if some regions were pooled rather than immediately released)
        assertTrue(bufferManager.getTotalReleased() > 0, "Some regions should be released during cleanup");
        assertEquals(allocatedBeforeCleanup, bufferManager.getTotalReleased(),