callback_router0 = APIRouter()


@callback_router0.get("/")
async def callback0(level0: str):
    pass  # pragma: nocover


callback_router1 = APIRouter()


@callback_router1.get("/")
async def callback1(level1: str):
    pass  # pragma: nocover


callback_router2 = APIRouter()


@callback_router2.get("/")
async def callback2(level2: str):
    pass  # pragma: nocover


callback_router3 = APIRouter()

app = FastAPI()


@app.get("/items/{item_id}")
def main(
    item_id: int = Path(default=..., gt=0),
    query: str = Query(default=..., max_length=10),
    session: str = Cookie(default=..., min_length=3),
    x_trace: str = Header(default=..., title="Tracing header"),
):
    return {"message": "Hello World"}
```

The non-blank variable names on the left side of <code>:=</code>
must be <a href="#Uniqueness_of_identifiers">unique</a>.
</p>

<pre>
field1, offset := nextField(str, 0)
field2, offset := nextField(str, offset)  // redeclares offset
x, y, x := 1, 2, 3                        // illegal: x repeated on left side of :=
</pre>

<p>
Short variable declarations may appear only inside functions.