So we are going to use that same knowledge to document how the *external API* should look like... by creating the *path operation(s)* that the external API should implement (the ones your API will call).

/// tip

When writing the code to document a callback, it might be useful to imagine that you are that *external developer*. And that you are currently implementing the *external API*, not *your API*.

            set(value) = Unit

        operator fun String.invoke(p: String, block: String.() -> Unit) = Unit

        ${""/* For Kotlin DSL, we generate sources with collection types mapped to the Kotlin ones. See `org.gradle.kotlin.dsl.internal.sharedruntime.codegen.ApiTypeProviderKt#mappedTypeStrings` */}

これらはすべて結合されて OpenAPI に含まれ、API ドキュメントに表示されます:

<img src="/img/tutorial/additional-responses/image01.png">

## 事前定義レスポンスとカスタムの組み合わせ { #combine-predefined-responses-and-custom-ones }

多くの *path operations* に適用できる事前定義のレスポンスを用意しつつ、各 *path operation* ごとに必要なカスタムレスポンスと組み合わせたい場合があります。

そのような場合、Python の `**dict_to_unpack` による `dict` の「アンパック」テクニックを使えます:

```Python
old_dict = {

    // have this Entry. The value in the map becomes false when this first entry has been copied, so
    // we know not to copy the remaining ones.
    IdentityHashMap<Entry<K, V>, Boolean> duplicates = null;
    int dupCount = 0;
    for (int entryIndex = n - 1; entryIndex >= 0; entryIndex--) {

        // spec says that we may repeat the request without modifications. Modern browsers also
        // repeat the request (even non-idempotent ones.)
        if (!chain.retryOnConnectionFailure) {
          // The application layer has directed us not to retry the request.
          return null
        }

        val requestBody = userResponse.request.body

You can check the currently [existing pull requests](https://github.com/fastapi/fastapi/pulls) for your language. You can filter the pull requests by the ones with the label for your language. For example, for Spanish, the label is [`lang-es`](https://github.com/fastapi/fastapi/pulls?q=is%3Aopen+sort%3Aupdated-desc+label%3Alang-es+label%3Aawaiting-review).

        excludedPackages.add("org.gradle.plugins.binaries.model");

        // Exclude classes that were moved in a different package but the deprecated ones are not removed yet
        excludedPackages.add("org.gradle.platform.base.test");
        return excludedPackages;
    }

   * under the assumption that for long-running instances, observed
   * contention levels will recur, so the cells will eventually be
   * needed again; and for short-lived ones, it does not matter.
   */

  /**
   * Padded variant of AtomicLong supporting only raw accesses plus CAS. The value field is placed
   * between pads, hoping that the JVM doesn't reorder them.
   *

---

**FastAPI** doesn't make any compromise with any database, data model or tool.

It gives you all the flexibility to choose the ones that fit your project the best.

And you can use directly many well maintained and widely used packages like `pwdlib` and `PyJWT`, because **FastAPI** doesn't require any complex mechanisms to integrate external packages.

- [AEAD](#aead): AES-256-GCM if the CPU supports AES-NI, ChaCha20-Poly1305 otherwise. More specifically AES-256-GCM is only selected for X86-64 CPUs with AES-NI extension.

Further any secret key (apart from the KMS-generated ones) is 256 bits long. The KMS-generated keys may be 256 bits but this depends on the KMS capabilities and configuration.