}
            }
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }
    }

    @Override
    public void putString(String source, Charset charset, URI relativeTarget) {
        requireNonNull(source, "source string is null");
        requireNonNull(charset, "charset is null");
        putBytes(source.getBytes(charset), relativeTarget);

We create an async function `lifespan()` with `yield` like this:

```Python hl_lines="16  19"
{!../../../docs_src/events/tutorial003.py!}
```

Here we are simulating the expensive *startup* operation of loading the model by putting the (fake) model function in the dictionary with machine learning models before the `yield`. This code will be executed **before** the application **starts taking requests**, during the *startup*.

  // The webhook cares about an operation if it matches _any_ Rule.
  // However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks
  // from putting the cluster in a state which cannot be recovered from without completely
  // disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called

  // The webhook cares about an operation if it matches _any_ Rule.
  // However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks
  // from putting the cluster in a state which cannot be recovered from without completely
  // disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called

    ```

### `Union` in Python 3.10

In this example we pass `Union[PlaneItem, CarItem]` as the value of the argument `response_model`.

Because we are passing it as a **value to an argument** instead of putting it in a **type annotation**, we have to use `Union` even in Python 3.10.

If it was in a type annotation we could have used the vertical bar, as:

```Python
some_variable: PlaneItem | CarItem
```

    public EntryComparator(@Nullable Comparator<? super K> keyComparator) {
      this.keyComparator = keyComparator;
    }

    @Override
    @SuppressWarnings("unchecked") // no less safe than putting it in the map!
    public int compare(Entry<K, V> a, Entry<K, V> b) {
      return (keyComparator == null)
          ? ((Comparable) a.getKey()).compareTo(b.getKey())
          : keyComparator.compare(a.getKey(), b.getKey());

    }

    @Override
    @ParametricNullness
    public T get() {
      // Another variant of Double Checked Locking.
      //
      // We use two volatile reads. We could reduce this to one by
      // putting our fields into a holder class, but (at least on x86)
      // the extra memory consumption and indirection are more
      // expensive than the extra volatile reads.
      long nanos = expirationNanos;

* It should not be client-specific.
  * In Istio sidecars, historically we had a lot of client-specific xDS. For example, putting the xDS-client's IP back into the xDS response. This makes efficient control plane implementation (most notably, caching), extremely challenging.

    public EntryComparator(@Nullable Comparator<? super K> keyComparator) {
      this.keyComparator = keyComparator;
    }

    @Override
    @SuppressWarnings("unchecked") // no less safe than putting it in the map!
    public int compare(Entry<K, V> a, Entry<K, V> b) {
      return (keyComparator == null)
          ? ((Comparable) a.getKey()).compareTo(b.getKey())
          : keyComparator.compare(a.getKey(), b.getKey());

    }

    @Override
    @ParametricNullness
    public T get() {
      // Another variant of Double Checked Locking.
      //
      // We use two volatile reads. We could reduce this to one by
      // putting our fields into a holder class, but (at least on x86)
      // the extra memory consumption and indirection are more
      // expensive than the extra volatile reads.
      long nanos = expirationNanos;