```Python hl_lines="2"
@app.get('/')
def results():
    results = some_library()
    return results
```

---

If your application (somehow) doesn't have to communicate with anything else and wait for it to respond, use `async def`, even if you don't need to use `await` inside.

---

If you just don't know, use normal `def`.

---

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():

from fastapi import FastAPI
from fastapi.responses import StreamingResponse

some_file_path = "large-video-file.mp4"
app = FastAPI()


@app.get("/")
def main():
    def iterfile():  # (1)
        with open(some_file_path, mode="rb") as file_like:  # (2)
            yield from file_like  # (3)

class PreparePatchReleaseIntegrationTest extends Specification {

    @TempDir
    File tmpDir

    def "version file is bumped and previous version is added to released versions"() {
        given:
        def versionFile = new File(tmpDir, "version.txt")
        versionFile.text = "9.4.0"

        def releasedVersionsFile = new File(tmpDir, "released-versions.json")
        releasedVersionsFile << '''{

from fastapi import FastAPI, Security
from fastapi.security import SecurityScopes
from fastapi.testclient import TestClient


async def security1(scopes: SecurityScopes):
    return scopes.scopes


async def security2(scopes: SecurityScopes):
    return scopes.scopes


async def dep3(
    dep1: Annotated[list[str], Security(security1, scopes=["scope1"])],
    dep2: Annotated[list[str], Security(security2, scopes=["scope2"])],

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/", tags=["items"])
async def read_items():
    return [{"name": "Foo", "price": 42}]


@app.get("/users/", tags=["users"])
async def read_users():
    return [{"username": "johndoe"}]


@app.get("/elements/", tags=["items"], deprecated=True)
async def read_elements():

    assertEquals(
        "getOrDefault(null, def) should return the default value",
        v3(),
        getMap().getOrDefault(null, v3()));
  }

  @MapFeature.Require(absent = ALLOWS_NULL_KEY_QUERIES)
  public void testGetOrDefault_nullAbsentAndUnsupported() {
    try {
      assertEquals(
          "getOrDefault(null, def) should return default or throw",
          v3(),

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"),
):

class RateLimiter:
    def __init__(self) -> None:
        self.last_query_cost: int = 1
        self.remaining_points: int = 5000
        self.reset_at: datetime = datetime.fromtimestamp(0, timezone.utc)
        self.last_request_start_time: datetime = datetime.fromtimestamp(0, timezone.utc)
        self.speed_multiplier: float = 1.0

    def __enter__(self) -> "RateLimiter":

    app = FastAPI()

    items = {"foo": "The Foo Wrestlers"}


    @app.get("/items/{item_id}")
    async def read_item(item_id: str):
        if item_id not in items:
            raise HTTPException(status_code=404, detail="Item not found")
        return {"item": items[item_id]}
    ```
    """

    def __init__(
        self,
        status_code: Annotated[
            int,
            Doc(
                """