當你在「大型程式碼庫」中，於許多「路徑操作」反覆使用「相同的依賴」時，這會特別有用。

## 要不要使用 `async` { #to-async-or-not-to-async }

因為依賴也會由 **FastAPI** 呼叫（就像你的「路徑操作函式」），所以在定義函式時套用相同的規則。

你可以使用 `async def` 或一般的 `def`。

而且你可以在一般 `def` 的「路徑操作函式」中宣告 `async def` 的依賴，或在 `async def` 的「路徑操作函式」中宣告 `def` 的依賴，等等。

都沒關係。**FastAPI** 會知道該怎麼做。

/// note | 注意

如果你不熟悉，請參考文件中的 [Async: "In a hurry?"](../../async.md#in-a-hurry) 一節，瞭解 `async` 與 `await`。

///

                    shortName = shortName.substring(shortName.lastIndexOf('/') + 1)
                }
                if (shortName.endsWith('.jar')) {
                    def outputDir = shortName.startsWith('gradle-') ? gradleJars : dependencies
                    def out = new File(outputDir, shortName)
                    Files.copy(zin, out.toPath())
                    zin.closeEntry()
                }
            }
        }
    }

).absolute()


@pytest.mark.parametrize(
    "copy_test_files",
    [(f"{data_path}/en_doc.md", f"{data_path}/translated_doc_mermaid_translated.md")],
    indirect=True,
)
def test_translated(runner: CliRunner, root_dir: Path, copy_test_files):
    result = runner.invoke(
        cli,
        ["fix-pages", "docs/lang/docs/doc.md"],
    )
    assert result.exit_code == 0, result.output

    description: str | None = None
    price: float
    tax: float | None = None
    tags: list[str] = []


@app.post("/items/", response_model=Item)
async def create_item(item: Item) -> Any:
    return item


@app.get("/items/", response_model=list[Item])
async def read_items() -> Any:
    return [
        {"name": "Portal Gun", "price": 42.0},
        {"name": "Plumbus", "price": 32.0},

Наприклад, ви можете оголосити, що щось може бути `str` або `None`:

```python
from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")
```

У `typing` також є скорочення, щоб оголосити, що щось може бути `None`, - `Optional`.

Ось порада з моєї дуже «суб'єктивної» точки зору:

    "path", ["/a/compute", "/a/compute/", "/b/compute", "/b/compute/"]
)
def test_post(path):
    data = {"a": 2, "b": "foo"}
    response = client.post(path, json=data)
    assert response.status_code == 200, response.text
    assert data == response.json()


@pytest.mark.parametrize(
    "path", ["/a/compute", "/a/compute/", "/b/compute", "/b/compute/"]
)
def test_post_invalid(path):
    data = {"a": "bar", "b": "foo"}

    region_name='us-east-1',
    use_ssl=False,
    endpoint_url='http://localhost:9000',
)

app = Flask(__name__)


@app.route('/')
def homepage():
    text = '<a href="%s">Authenticate with keycloak</a>'
    return text % make_authorization_url()


def make_authorization_url():
    # Generate a random string for the state parameter
    # Save it for use later to prevent xsrf attacks

    state = str(uuid4())

fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: str | None = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons: CommonQueryParams = Depends(CommonQueryParams)):
    response = {}
    if commons.q:

fake_items_db = [{"item_name": "Foo"}, {"item_name": "Bar"}, {"item_name": "Baz"}]


class CommonQueryParams:
    def __init__(self, q: str | None = None, skip: int = 0, limit: int = 100):
        self.q = q
        self.skip = skip
        self.limit = limit


@app.get("/items/")
async def read_items(commons: CommonQueryParams = Depends()):
    response = {}
    if commons.q:
        response.update({"q": commons.q})

You can use `async def` or normal `def`.

And you can declare dependencies with `async def` inside of normal `def` *path operation functions*, or `def` dependencies inside of `async def` *path operation functions*, etc.

It doesn't matter. **FastAPI** will know what to do.

/// note