// If we successfully add the computed element, we're done.
    val newTags = tags.plus(type, computed)
    if (compareAndSet(tags, newTags)) return computed

    // We lost the race. Possibly to other code that was putting a *different* key. Try again!
  }

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

{* ../../docs_src/events/tutorial003_py39.py hl[16,19] *}

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*.

### `Union` in Python 3.10 { #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
```

  for (i in 0 until length) {
    val c = this[i]
    if (c <= '\u001f' || c >= '\u007f') {
      return i
    }
  }
  return -1
}

/** Returns true if we should void putting this this header in an exception or toString(). */
internal fun isSensitiveHeader(name: String): Boolean =
  name.equals("Authorization", ignoreCase = true) ||
    name.equals("Cookie", ignoreCase = true) ||

        end = srcIndex + this.rDataLength;
        /*
         * Apparently readRDataWireFormat can return 0 if resultCode != 0 in
         * which case this will look indefinitely. Putting this else clause around
         * the loop might fix that. But I would need to see a capture to confirm.
         * if (resultCode != 0) {
         * srcIndex += rDataLength;
         * } else {
         */

        addrEntry = new NbtAddress[rDataLength / 6];
        end = srcIndex + rDataLength;
        /* Apparently readRDataWireFormat can return 0 if resultCode != 0 in
        which case this will look indefinitely. Putting this else clause around
        the loop might fix that. But I would need to see a capture to confirm.
        if (resultCode != 0) {
            srcIndex += rDataLength;
        } else {
        */

    /**
     * Default mode for combining children DOMs during merge.
     * When element names match, the process will try to merge the element data,
     * rather than putting the dominant and recessive elements as siblings.
     */
    public static final String DEFAULT_CHILDREN_COMBINATION_MODE = CHILDREN_COMBINATION_MERGE;

    /** Attribute name controlling how the element itself is combined */

    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());

    /**
     * This default mode for combining children DOMs during merge means that where element names match, the process will
     * try to merge the element data, rather than putting the dominant and recessive elements (which share the same
     * element name) as siblings in the resulting DOM.
     */
    @Deprecated(since = "4.0.0", forRemoval = true)

Previous versions of FastAPI (before <abbr title="before 2023-03">0.95.0</abbr>) required you to use `Query` as the default value of your parameter, instead of putting it in `Annotated`, there's a high chance that you will see code using it around, so I'll explain it to you.

/// tip