**FastAPI** 🔜 🚧 🌖 ℹ ⚪️➡️ `responses`, & 🌀 ⚫️ ⏮️ 🎻 🔗 ⚪️➡️ 👆 🏷.

🖼, 👆 💪 📣 📨 ⏮️ 👔 📟 `404` 👈 ⚙️ Pydantic 🏷 & ✔️ 🛃 `description`.

& 📨 ⏮️ 👔 📟 `200` 👈 ⚙️ 👆 `response_model`, ✋️ 🔌 🛃 `example`:

```Python hl_lines="20-31"
{!../../docs_src/additional_responses/tutorial003.py!}
```

⚫️ 🔜 🌐 🌀 & 🔌 👆 🗄, & 🎦 🛠️ 🩺:

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

    if (!hasNext()) throw NoSuchElementException()

    // Compute the next set of routes to attempt.
    val routes = mutableListOf<Route>()
    while (hasNextProxy()) {
      // Postponed routes are always tried last. For example, if we have 2 proxies and all the
      // routes for proxy1 should be postponed, we'll move to proxy2. Only after we've exhausted
      // all the good routes will we attempt the postponed routes.
      val proxy = nextProxy()

 * ordinarily difficult to write iterators for. But using this class, one must implement only the
 * {@link #computeNext} method, and invoke the {@link #endOfData} method when appropriate.
 *
 * <p>Another example is an iterator that skips over null elements in a backing iterator. This could
 * be implemented as:
 *
 * <pre>{@code
 * public static Iterator<String> skipNulls(final Iterator<String> in) {

## 🔬 ⏲

☑ ⏲ 📟 🔜 🪀 🙇 🔛 👆 👍 🛠️ 📱.

& ⚫️ 🔜 🎲 🪀 📚 ⚪️➡️ 1️⃣ 📱 ⏭.

⚫️ 💪 1️⃣ ⚖️ 2️⃣ ⏸ 📟, 💖:

```Python
callback_url = "https://example.com/api/v1/invoices/events/"
httpx.post(callback_url, json={"description": "Invoice paid", "paid": True})
```

✋️ 🎲 🏆 ⚠ 🍕 ⏲ ⚒ 💭 👈 👆 🛠️ 👩‍💻 (🔢 👩‍💻) 🛠️ *🔢 🛠️* ☑, 🛄 💽 👈 *👆 🛠️* 🔜 📨 📨 💪 ⏲, ♒️.

Just use any kind of model, any kind of class, any kind of database that you need for your application. **FastAPI** has you covered with the dependency injection system.

## Code size

This example might seem verbose. Keep in mind that we are mixing security, data models, utility functions and *path operations* in the same file.

But here's the key point.

The security and dependency injection stuff is written once.

    )
    assert response.status_code == 200, response.text
    assert response.json() == {
        "username": "johndoe",
        "full_name": "John Doe",
        "email": "johndoe@example.com",
        "disabled": False,
    }


@needs_py310
def test_incorrect_token(client: TestClient):
    response = client.get("/users/me", headers={"Authorization": "Bearer nonexistent"})

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An immutable builder for {@link Multimap} instances, letting you independently select the desired
 * behaviors (for example, ordering) of the backing map and value-collections. Example:
 *
 * <pre>{@code
 * ListMultimap<UserId, ErrorResponse> errorsByUser =
 *     MultimapBuilder.linkedHashKeys().arrayListValues().build();
 * SortedSetMultimap<String, Method> methodsForName =

      if (array[i] == target) {
        return i;
      }
    }
    return -1;
  }

  /**
   * Returns the values from each provided array combined into a single array. For example, {@code
   * concat(new byte[] {a, b}, new byte[] {}, new byte[] {c}} returns the array {@code {a, b, c}}.
   *
   * @param arrays zero or more {@code byte} arrays

Mas ainda assim, é bastante poderoso, e permite que você declare grafos (árvores) de dependências com uma profundidade arbitrária.

/// tip | "Dica"

Tudo isso pode não parecer muito útil com esses exemplos.

Mas você verá o quão útil isso é nos capítulos sobre **segurança**.

E você também verá a quantidade de código que você não precisara escrever.

    doTestTrimFrom("x--x", "x--x");
    doTestTrimFrom("x-x-", "x-x");
    doTestTrimFrom("x-xx", "x-xx");
    doTestTrimFrom("x-x--xx---x----x", "x-x--xx---x----x");
    // additional testing using the doc example
    assertEquals("cat", anyOf("ab").trimFrom("abacatbab"));
  }

  private void doTestTrimFrom(String in, String out) {
    // Try a few different matchers which all match '-' and not 'x'