def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>Tàbí lò <code>async def</code>...</summary>

Tí kóòdù rẹ̀ bá ń lò `async` / `await`, lò `async def`:

```Python hl_lines="9  14"
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def read_root():
    return {"Hello": "World"}

                } catch (Exception e) {
                    success[index] = false;
                }
            });
            threads[i].start();
        }

        // Wait for all threads to complete
        for (Thread thread : threads) {
            thread.join();
        }

        // All threads should complete successfully
        for (boolean s : success) {

            });
        }

        // Start all threads
        for (Thread thread : threads) {
            thread.start();
        }

        // Wait for all threads to complete
        for (Thread thread : threads) {
            thread.join();
        }

        // All results should be the same
        String expectedValue = "Test Fess";

                } else {
                    latch.countDown();
                }
            }
            try {
                latch.await();
            } catch (InterruptedException e) {
                result.addErrorArtifactException(
                        new ArtifactResolutionException("Resolution interrupted", rootArtifact, e));
            }

                // Remove the waiter, one way or another we are done parking this thread.
                removeWaiter(node);
                break long_wait_loop; // jump down to the busy wait loop
              }
            }
          }
          oldHead = waitersField; // re-read and loop.
        } while (oldHead != Waiter.TOMBSTONE);
      }

/// tip

Notice that here as we are using standard `open()` that doesn't support `async` and `await`, we declare the path operation with normal `def`.

///

### `FileResponse` { #fileresponse }

Asynchronously streams a file as the response.

        for (WitnessRegistration registration : registrations.values()) {
            unregisterFutures.add(unregister(registration));
        }

        // Wait for all unregistrations to complete
        try {
            CompletableFuture.allOf(unregisterFutures.toArray(new CompletableFuture[0])).get(10, TimeUnit.SECONDS);
        } catch (Exception e) {

**reflected** on the client code automatically. And if you **build** the client, it will error out if you have any **mismatch** in the data used.

So, you would **detect many errors** very early in the development cycle instead of having to wait for the errors to show up to your final users in production and then trying to debug where the problem is. ✨...

    assertSame(exception, e.getCause());
  }

  private static void awaitUnchecked(CyclicBarrier barrier) {
    try {
      barrier.await();
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }

  private void checkStackTrace(ExecutionException e) {
    // Our call site for get() should be in the trace.

				throw new Error("total length of command line and environment variables exceeds limit");
			}

			this._inst.exports.run(argc, argv);
			if (this.exited) {
				this._resolveExitPromise();
			}
			await this._exitPromise;
		}

		_resume() {
			if (this.exited) {
				throw new Error("Go program has already exited");
			}
			this._inst.exports.resume();
			if (this.exited) {