When you create a **FastAPI** *path operation* you can normally return any data from it: a `dict`, a `list`, a Pydantic model, a database model, etc.

By default, **FastAPI** would automatically convert that return value to JSON using the `jsonable_encoder` explained in [JSON Compatible Encoder](../tutorial/encoder.md){.internal-link target=_blank}.

headers can be added <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">using the 'X-' prefix</a>.

But if you have custom headers that you want a client in a browser to be able to see, you need to add them to your CORS configurations ([CORS (Cross-Origin Resource Sharing)](cors.md){.internal-link target=_blank}) using the parameter `expose_headers` documented in <a href="https://www.starlette.io/middleware/#corsmiddleware" class="external-link"...

   * AssertionFailedError thrown, so that the current testcase will fail.
   */
  public void threadAssertFalse(boolean b) {
    try {
      assertFalse(b);
    } catch (AssertionFailedError t) {
      threadRecordFailure(t);
      throw t;
    }
  }

  /**
   * Just like assertNull(x), but additionally recording (using threadRecordFailure) any

 * implementation.
 */
@GwtIncompatible
public class NavigableMapTestSuiteBuilder<K, V> extends SortedMapTestSuiteBuilder<K, V> {
  public static <K, V> NavigableMapTestSuiteBuilder<K, V> using(
      TestSortedMapGenerator<K, V> generator) {
    NavigableMapTestSuiteBuilder<K, V> result = new NavigableMapTestSuiteBuilder<>();
    result.usingGenerator(generator);
    return result;
  }

In an advanced scenario where you know you need the dependency to be called at every step (possibly multiple times) in the same request instead of using the "cached" value, you can set the parameter `use_cache=False` when using `Depends`:

//// tab | Python 3.8+

```Python hl_lines="1"
async def needy_dependency(fresh_value: Annotated[str, Depends(get_value, use_cache=False)]):

Layers Layer Number of classes Classes of layer : Classes and Packages Click on or to go to the cycle to which the class/package belongs. Class/Package Size Used by Uses internal Uses external Layer Source(s) # Member of cycle Classes using : uses: true uses: Packages using : uses: true uses: Classes of cycle : Best fragmenter(s) of cycle : Center classes of cycle : Packages of cycle : Best fragmenter(s) of cycle : Center packages of cycle : cursor:pointer; javascript:showTable(" ",""," ; ") cursor:pointer;...

    ujson = None  # type: ignore


try:
    import orjson
except ImportError:  # pragma: nocover
    orjson = None  # type: ignore


class UJSONResponse(JSONResponse):
    """
    JSON response using the high-performance ujson library to serialize data to JSON.

    Read more about it in the
    [FastAPI docs for Custom Response - HTML, Stream, File, others](https://fastapi.tiangolo.com/advanced/custom-response/).
    """

But at some point, there was no other option than creating something that provided all these features, taking the best ideas from previous tools, and combining them in the best way possible, using language features that weren't even available before (Python 3.6+ type hints).

</blockquote>

            .named("ImmutableMap.entrySet.asList")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.REJECTS_DUPLICATES_AT_CREATION,
                CollectionFeature.ALLOWS_NULL_QUERIES)
            .createTestSuite());

    suite.addTest(

   *       byte is then represented by the 3-character string "%XY", where "XY" is the two-digit,
   *       uppercase, hexadecimal representation of the byte value.
   * </ul>
   *
   * <p>This escaper is suitable for escaping parameter names and values even when <a
   * href="https://www.w3.org/TR/html401/appendix/notes.html#h-B.2.2">using the non-standard