Die Statuscodes im 400er-Bereich bedeuten hingegen, dass es einen Fehler gab.

Erinnern Sie sich an all diese **404 Not Found** Fehler (und Witze)?

## `HTTPException` verwenden

Um HTTP-Responses mit Fehlern zum Client zurückzugeben, verwenden Sie `HTTPException`.

### `HTTPException` importieren

```Python hl_lines="1"

        # The hero is no longer found
        response = client.get(f"/heroes/{hero_id}")
        assert response.status_code == 404, response.text

        # Delete a hero that does not exist
        response = client.delete(f"/heroes/{hero_id}")
        assert response.status_code == 404, response.text
        assert response.json() == snapshot({"detail": "Hero not found"})

        # Update a hero that does not exist

        raise InternalError(
            f"The portal gun is too dangerous to be owned by {username}"
        )
    if item_id != "plumbus":
        raise HTTPException(
            status_code=404, detail="Item not found, there's only a plumbus here"
        )

    assert response.json() == {"detail": "Invalid X-Token header"}


def test_read_nonexistent_item():
    response = client.get("/items/baz", headers={"X-Token": "coneofsilence"})
    assert response.status_code == 404
    assert response.json() == {"detail": "Item not found"}


def test_create_item():
    response = client.post(
        "/items/",
        headers={"X-Token": "coneofsilence"},

    assert response.json() == {"detail": "Invalid X-Token header"}


def test_read_nonexistent_item():
    response = client.get("/items/baz", headers={"X-Token": "coneofsilence"})
    assert response.status_code == 404
    assert response.json() == {"detail": "Item not found"}


def test_create_item():
    response = client.post(
        "/items/",
        headers={"X-Token": "coneofsilence"},

    Listener listener;
    synchronized (this) {
      listener = listeners.get(state);
    }

    if (code == null || listener == null) {
      return new MockResponse()
          .setResponseCode(404)
          .setBody("unexpected request");
    }

    try {
      OAuthSession session = slackApi.exchangeCode(code, redirectUrl());
      listener.sessionGranted(session);
    } catch (IOException e) {

需要向客户端返回错误提示的场景主要如下：

- 客户端没有执行操作的权限
- 客户端没有访问资源的权限
- 客户端要访问的项目不存在
- 等等 ...

遇到这些情况时，通常要返回 **4XX**（400 至 499）**HTTP 状态码**。

**4XX** 状态码与表示请求成功的 **2XX**（200 至 299） HTTP 状态码类似。

只不过，**4XX** 状态码表示客户端发生的错误。

大家都知道**「404 Not Found」**错误，还有调侃这个错误的笑话吧？

## 使用 `HTTPException`

向客户端返回 HTTP 错误响应，可以使用 `HTTPException`。

### 导入 `HTTPException`

```Python hl_lines="1"
{!../../docs_src/handling_errors/tutorial001.py!}

```

                }
                if (httpStatusCode == 404) {
                    storeChildUrlsToQueue(urlQueue, getAnchorSet(document.get(fessConfig.getIndexFieldAnchor())));
                    if (!indexingHelper.deleteDocument(searchEngineClient, id)) {
                        logger.debug("Failed to delete 404 document: {}", url);
                    }
                    return false;
                }

    client = TestClient(app)
    return client


def test_get_no_item(client: TestClient):
    response = client.get("/items/foo")
    assert response.status_code == 404, response.text
    assert response.json() == {"detail": "Item not found, there's only a plumbus here"}


def test_get(client: TestClient):
    response = client.get("/items/plumbus")

    if x_token != fake_secret_token:
        raise HTTPException(status_code=400, detail="Invalid X-Token header")
    if item_id not in fake_db:
        raise HTTPException(status_code=404, detail="Item not found")
    return fake_db[item_id]


@app.post("/items/", response_model=Item)
async def create_item(item: Item, x_token: str = Header()):
    if x_token != fake_secret_token: