<mxfile host="65bd71144e">
    <diagram id="jyERGzDynktFHFRGN0ph" name="Page-1">
        <mxGraphModel dx="2738" dy="2173" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="1920" pageHeight="1200" math="0" shadow="0">
            <root>
                <mxCell id="0"/>
                <mxCell id="1" parent="0"/>

And then you can also have a path `/users/{user_id}` to get data about a specific user by some user ID.

Because *path operations* are evaluated in order, you need to make sure that the path for `/users/me` is declared before the one for `/users/{user_id}`:

```Python hl_lines="6  11"
{!../../../docs_src/path_params/tutorial003.py!}
```

有时，*路径操作*中的路径是写死的。

比如要使用 `/users/me` 获取当前用户的数据。

然后还要使用 `/users/{user_id}`，通过用户 ID 获取指定用户的数据。

由于*路径操作*是按顺序依次运行的，因此，一定要在 `/users/{user_id}` 之前声明 `/users/me` ：

```Python hl_lines="6  11"
{!../../../docs_src/path_params/tutorial003.py!}
```

否则，`/users/{user_id}` 将匹配 `/users/me`，FastAPI 会**认为**正在接收值为 `"me"` 的 `user_id` 参数。

## 预设值

路径操作使用 Python 的 <abbr title="Enumeration">`Enum`</abbr> 类型接收预设的*路径参数*。

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Optional[str] = None):
    return {"item_id": item_id, "q": q}
```

* Vous devriez maintenant avoir une structure de répertoire telle que :

```
.
├── app
│   └── main.py
└── Dockerfile
```

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

```Python hl_lines="11"
{!../../../docs_src/handling_errors/tutorial001.py!}

```

### 响应结果

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"
}

```

    ```Python hl_lines="1"
    {!> ../../../docs_src/path_params_numeric_validations/tutorial001_py310.py!}
    ```

## 📣 🗃

👆 💪 📣 🌐 🎏 🔢 `Query`.

🖼, 📣 `title` 🗃 💲 ➡ 🔢 `item_id` 👆 💪 🆎:

=== "🐍 3️⃣.6️⃣ & 🔛"

    ```Python hl_lines="10"
    {!> ../../../docs_src/path_params_numeric_validations/tutorial001.py!}
    ```

=== "🐍 3️⃣.1️⃣0️⃣ & 🔛"

    ```Python hl_lines="8"

In diesem Fall ist es der `str`:

```Python
"{$callback_url}/invoices/{$request.body.id}"
```

Wenn Ihr API-Benutzer (der externe Entwickler) also einen Request an *Ihre API* sendet, via:

```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

mit einem JSON-Körper:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

👉 💼, ⚫️ `str`:

```Python
"{$callback_url}/invoices/{$request.body.id}"
```

, 🚥 👆 🛠️ 👩‍💻 (🔢 👩‍💻) 📨 📨 *👆 🛠️* :

```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

⏮️ 🎻 💪:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

            },
            "Item": {
                "title": "Item",
                "required": [
                    "id",
                    "value"
                ],
                "type": "object",
                "properties": {
                    "id": {
                        "title": "Id",
                        "type": "string"
                    },
                    "value": {

{!../../../docs_src/handling_errors/tutorial001.py!}
```

### 📉 📨

🚥 👩‍💻 📨 `http://example.com/items/foo` ( `item_id` `"foo"`), 👈 👩‍💻 🔜 📨 🇺🇸🔍 👔 📟 2️⃣0️⃣0️⃣, & 🎻 📨:

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

✋️ 🚥 👩‍💻 📨 `http://example.com/items/bar` (🚫-🚫 `item_id` `"bar"`), 👈 👩‍💻 🔜 📨 🇺🇸🔍 👔 📟 4️⃣0️⃣4️⃣ ("🚫 🔎" ❌), & 🎻 📨:

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