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


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


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    return {"item_name": item.name, "item_id": item_id}
```

@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}


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    return {"item_name": item.name, "item_id": item_id}
```

from pydantic import BaseModel


class User(BaseModel):
    id: int
    name: str = "John Doe"
    signup_ts: Union[datetime, None] = None
    friends: List[int] = []


external_data = {
    "id": "123",
    "signup_ts": "2017-06-01 12:22",
    "friends": [1, "2", b"3"],
}
user = User(**external_data)
print(user)
# > User id=123 name='John Doe' signup_ts=datetime.datetime(2017, 6, 1, 12, 22) friends=[1, 2, 3]

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            examples=[
                {
                    "name": "Foo",
                    "description": "A very nice Item",

app = FastAPI()


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            examples=[
                {
                    "name": "Foo",
                    "description": "A very nice Item",

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


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


@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    return {"item_name": item.name, "item_id": item_id}
```

服务器将会自动重载（因为在上面的步骤中你向 `uvicorn` 命令添加了 `--reload` 选项）。

### 交互式 API 文档升级

            assert data == f"Message text was: {message}, for item ID: foo"
            message = "Message two"
            websocket.send_text(message)
            data = websocket.receive_text()
            assert data == "Session cookie or query token value is: fakesession"
            data = websocket.receive_text()
            assert data == f"Message text was: {message}, for item ID: foo"


@needs_py310

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!}
```

У вас также может быть путь `/users/{user_id}`, чтобы получить данные о конкретном пользователе по его ID.

Поскольку *операции пути* выполняются в порядке их объявления, необходимо, чтобы путь для `/users/me` был объявлен раньше, чем путь для `/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*。