## `async` oder nicht `async` { #to-async-or-not-to-async }

Da Abhängigkeiten auch von **FastAPI** aufgerufen werden (so wie Ihre *Pfadoperation-Funktionen*), gelten beim Definieren Ihrer Funktionen die gleichen Regeln.

Sie können `async def` oder einfach `def` verwenden.

import anyio
from fastapi import FastAPI
from fastapi.responses import StreamingResponse

app = FastAPI()


async def fake_video_streamer():
    for i in range(10):
        yield b"some fake video bytes"
        await anyio.sleep(0)


@app.get("/")
async def main():

app = FastAPI()
router = APIRouter()


@router.get("/a", responses={501: {"description": "Error 1"}})
async def a():
    return "a"


@router.get(
    "/b",
    responses={
        502: {"description": "Error 2"},
        "4XX": {"description": "Error with range, upper"},
    },
)
async def b():
    return "b"


@router.get(
    "/c",
    responses={

class Model(BaseModel):
    param: str

    model_config = {"extra": "allow"}


@app.get("/query")
async def query_model_with_extra(data: Model = Query()):
    return data


@app.get("/header")
async def header_model_with_extra(data: Model = Header()):
    return data


@app.get("/cookie")
async def cookies_model_with_extra(data: Model = Cookie()):
    return data


def test_query_pass_extra_list():

from fastapi import FastAPI, File, UploadFile

app = FastAPI()


@app.post("/files/")
async def create_file(file: bytes = File(description="A file read as bytes")):
    return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(
    file: UploadFile = File(description="A file read as UploadFile"),
):

import pytest
from httpx import ASGITransport, AsyncClient

from .main import app


@pytest.mark.anyio
async def test_root():
    async with AsyncClient(
        transport=ASGITransport(app=app), base_url="http://test"
    ) as ac:
        response = await ac.get("/")
    assert response.status_code == 200

from fastapi import FastAPI

app = FastAPI()


class Tags(Enum):
    items = "items"
    users = "users"


@app.get("/items/", tags=[Tags.items])
async def get_items():
    return ["Portal gun", "Plumbus"]


@app.get("/users/", tags=[Tags.users])
async def read_users():

8. Bu *path operation function*, `async def` yerine normal `def` kullanıyor.

    Her zaman olduğu gibi, FastAPI'de ihtiyaca göre `def` ve `async def`’i birlikte kullanabilirsiniz.

    Hangisini ne zaman kullanmanız gerektiğine dair hızlı bir hatırlatma isterseniz, [`async` ve `await`](../async.md#in-a-hurry) dokümanındaki _"In a hurry?"_ bölümüne bakın.

                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


async def get_cookie_or_token(
    websocket: WebSocket,
    session: Annotated[str | None, Cookie()] = None,
    token: Annotated[str | None, Query()] = None,
):

                input.value = ''
                event.preventDefault()
            }
        </script>
    </body>
</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


async def get_cookie_or_token(
    websocket: WebSocket,
    session: str | None = Cookie(default=None),
    token: str | None = Query(default=None),
):
    if session is None and token is None: