from fastapi import FastAPI, File, UploadFile

app = FastAPI()


@app.post("/files/")
async def create_file(file: Union[bytes, None] = File(default=None)):
    if not file:
        return {"message": "No file sent"}
    else:
        return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(file: Union[UploadFile, None] = None):
    if not file:

只要把它传递给 `Depends`，**FastAPI** 就知道该如何执行后续操作。

///

## 要不要使用 `async`？

**FastAPI** 调用依赖项的方式与*路径操作函数*一样，因此，定义依赖项函数，也要应用与路径操作函数相同的规则。

即，既可以使用异步的 `async def`，也可以使用普通的 `def` 定义依赖项。

在普通的 `def` *路径操作函数*中，可以声明异步的 `async def` 依赖项；也可以在异步的 `async def` *路径操作函数*中声明普通的 `def` 依赖项。

上述这些操作都是可行的，**FastAPI** 知道该怎么处理。

/// note | "笔记"

如里不了解异步，请参阅[异步：*“着急了？”*](../../async.md){.internal-link target=_blank} 一章中 `async` 和 `await` 的内容。

                "tax": 10.5,
                "tags": [],
            },
        ),
    ],
)
def test_get(url, data, client: TestClient):
    response = client.get(url)
    assert response.status_code == 200, response.text
    assert response.json() == data


@needs_py310
def test_openapi_schema(client: TestClient):
    response = client.get("/openapi.json")

from fastapi import FastAPI

app = FastAPI()


@app.get("/users/me")
async def read_user_me():
    return {"user_id": "the current user"}


@app.get("/users/{user_id}")
async def read_user(user_id: str):

app = FastAPI()


@sub_router.get("/")
def read_item():
    return {"id": "foo"}


router.include_router(sub_router, prefix="/items")

app.include_router(router)

client = TestClient(app)


def test_path_operation():
    response = client.get("/items/")
    assert response.status_code == 200, response.text
    assert response.json() == {"id": "foo"}


def test_openapi_schema():

@app.get("/app")
def read_main(request: Request):
    return {"message": "Hello World", "root_path": request.scope.get("root_path")}


client = TestClient(app)


def test_main():
    response = client.get("/app")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World", "root_path": "/api/v1"}


def test_openapi():
    response = client.get("/openapi.json")

app = FastAPI()


@app.exception_handler(StarletteHTTPException)
async def custom_http_exception_handler(request, exc):
    print(f"OMG! An HTTP error!: {repr(exc)}")
    return await http_exception_handler(request, exc)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")

    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},

from fastapi import FastAPI

app = FastAPI()


@app.on_event("shutdown")
def shutdown_event():
    with open("log.txt", mode="a") as log:
        log.write("Application shutdown")


@app.get("/items/")
async def read_items():

from ...utils import needs_py310, needs_pydanticv1, needs_pydanticv2


@pytest.fixture(name="client")
def get_client():
    from docs_src.path_operation_configuration.tutorial005_py310 import app

    client = TestClient(app)
    return client


@needs_py310
def test_query_params_str_validations(client: TestClient):
    response = client.post("/items/", json={"name": "Foo", "price": 42})