@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):
    if item_id == "portal-gun":
        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"
        )

在介绍依赖项与安全的章节中，你可以更直观地看到用 `raise` 异常代替 `return` 值的优势。

本例中，客户端用不存在的 `ID` 请求 `item` 时，触发状态码为 `404` 的异常：

{* ../../docs_src/handling_errors/tutorial001_py310.py hl[11] *}

### 响应结果 { #the-resulting-response }

请求为 `http://example.com/items/foo`（`item_id` 为 `"foo"`）时，客户端会接收到 HTTP 状态码 200 及如下 JSON 响应结果：

```JSON
{
  "item": "The Foo Wrestlers"
}
```

from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(q: str, item_id: int = Path(title="The ID of the item to get")):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})

```JSON
{
  "item": "The Foo Wrestlers"
}
```

Pero si el cliente solicita `http://example.com/items/bar` (un `item_id` inexistente `"bar"`), ese cliente recibirá un código de estado HTTP de 404 (el error "no encontrado"), y un response JSON de:

```JSON
{
  "detail": "Item not found"
}
```

/// tip | Consejo

```JSON
{
  "item": "The Foo Wrestlers"
}
```

Mas se o cliente faz uma requisição para `http://example.com/items/bar` (ou seja, um não existente `item_id "bar"`), esse cliente receberá um HTTP status code 404 (o erro "não encontrado" — *not found error*), e uma resposta JSON:

```JSON
{
  "detail": "Item not found"
}
```

/// tip | Dica

#d6d8db;\n}\n\n.list-group-item-secondary.list-group-item-action:hover, .list-group-item-secondary.list-group-item-action:focus {\n  color: #383d41;\n  background-color: #c8cbcf;\n}\n\n.list-group-item-secondary.list-group-item-action.active {\n  color: #fff;\n  background-color: #383d41;\n  border-color: #383d41;\n}\n\n.list-group-item-success {\n  color: #155724;\n  background-color: #c3e6cb;\n}\n\n.list-group-item-success.list-group-item-action:hover, .list-group-item-success.list-group-item-action:focus {\n...

{* ../../docs_src/query_params_str_validations/tutorial008_an_py310.py hl[14] *}

## 別名參數 { #alias-parameters }

想像你希望參數名稱是 `item-query`。

像這樣：

```
http://127.0.0.1:8000/items/?item-query=foobaritems
```

但 `item-query` 不是合法的 Python 變數名稱。

最接近的大概是 `item_query`。

但你仍然需要它就是 `item-query`...

那你可以宣告一個 `alias`，實際上就會用這個別名來讀取參數值：

												<la:message key="labels.profile" />
											</la:link>
										</c:if>
										<c:if test="${adminUser == true}">
											<la:link href="/admin" styleClass="dropdown-item">
												<la:message key="labels.administration" />
											</la:link>
										</c:if>
										<la:link href="/logout/" styleClass="dropdown-item">
											<la:message key="labels.logout" />

												<la:message key="labels.profile" />
											</la:link>
										</c:if>
										<c:if test="${adminUser == true}">
											<la:link href="/admin" styleClass="dropdown-item">
												<la:message key="labels.administration" />
											</la:link>
										</c:if>
										<la:link href="/logout/" styleClass="dropdown-item">
											<la:message key="labels.logout" />

from typing import Annotated

from fastapi import FastAPI, Path

app = FastAPI()


@app.get("/items/{item_id}")
async def read_items(
    item_id: Annotated[int, Path(title="The ID of the item to get", ge=1)], q: str
):
    results = {"item_id": item_id}
    if q:
        results.update({"q": q})