async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")
    return await request_validation_exception_handler(request, exc)


@app.get("/items/{item_id}")
async def read_item(item_id: int):
    if item_id == 3:
        raise HTTPException(status_code=418, detail="Nope! I don't like 3.")

So, the section with:

{% raw %}

```jinja
<a href="{{ url_for('read_item', id=id) }}">
```

{% endraw %}

...will generate a link to the same URL that would be handled by the *path operation function* `read_item(id=id)`.

For example, with an ID of `42`, this would render:

```html
<a href="/items/42">
```

```html
Item ID: 42
```

### 模板 `url_for` 参数

你还可以在模板内使用 `url_for()`，其参数与*路径操作函数*的参数相同.

所以，该部分:

{% raw %}

```jinja
<a href="{{ url_for('read_item', id=id) }}">
```

{% endraw %}

...将生成一个与处理*路径操作函数* `read_item(id=id)`的URL相同的链接

例如。当ID为 `42`时, 会渲染成:

```html
<a href="/items/42">
```

## 模板与静态文件

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_item(item_id: str, q: str | None = None, short: bool = False):
    item = {"item_id": item_id}
    if q:
        item.update({"q": q})
    if not short:
        item.update(
            {"description": "This is an amazing item that has a long description"}
        )

    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item)
async def read_item(item_id: str):
    return items[item_id]


@app.put("/items/{item_id}", response_model=Item)
async def update_item(item_id: str, item: Item):
    update_item_encoded = jsonable_encoder(item)

    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item)
async def read_item(item_id: str):
    return items[item_id]


@app.patch("/items/{item_id}", response_model=Item)
async def update_item(item_id: str, item: Item):
    stored_item_data = items[item_id]

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_item(item_id: int):

    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}


@app.get("/items/{item_id}", response_model=Item)
async def read_item(item_id: str):
    return items[item_id]


@app.patch("/items/{item_id}", response_model=Item)
async def update_item(item_id: str, item: Item):
    stored_item_data = items[item_id]

}


app = FastAPI()


@app.get(
    "/items/{item_id}",
    response_model=Item,
    responses={**responses, 200: {"content": {"image/png": {}}}},
)
async def read_item(item_id: str, img: Union[bool, None] = None):
    if img:
        return FileResponse("image.png", media_type="image/png")
    else:

from typing import Union

from fastapi import FastAPI

app = FastAPI()


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