class Session:
    def __init__(self) -> None:
        self.data = ["foo", "bar", "baz"]
        self.open = True

    def __iter__(self) -> Generator[str, None, None]:
        for item in self.data:
            if self.open:
                yield item
            else:
                raise ValueError("Session closed")


@contextmanager
def acquire_session() -> Generator[Session, None, None]:
    session = Session()
    try:

Le paramètre de requête `q` a pour type `Union[str, None]` (ou `str | None` en Python 3.10), signifiant qu'il est de type `str` mais pourrait aussi être égal à `None`, et bien sûr, la valeur par défaut est `None`, donc **FastAPI** saura qu'il n'est pas requis.

/// note

**FastAPI** saura que la valeur de `q` n'est pas requise grâce à la valeur par défaut `= None`.

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


async def get_cookie_or_token(
    websocket: WebSocket,
    session: Annotated[Union[str, None], Cookie()] = None,
    token: Annotated[Union[str, None], Query()] = None,
):
    if session is None and token is None:
        raise WebSocketException(code=status.WS_1008_POLICY_VIOLATION)
    return session or token


@app.websocket("/items/{item_id}/ws")

    access_token: str
    token_type: str


class TokenData(BaseModel):
    username: Union[str, None] = None
    scopes: list[str] = []


class User(BaseModel):
    username: str
    email: Union[str, None] = None
    full_name: Union[str, None] = None
    disabled: Union[bool, None] = None


class UserInDB(User):
    hashed_password: str


password_hash = PasswordHash.recommended()

@app.post("/optional-list-str", operation_id="optional_list_str")
async def read_optional_list_str(
    p: Annotated[Optional[list[str]], Form()] = None,
):
    return {"p": p}


class FormModelOptionalListStr(BaseModel):
    p: Optional[list[str]] = None


@app.post("/model-optional-list-str", operation_id="model_optional_list_str")
async def read_model_optional_list_str(p: Annotated[FormModelOptionalListStr, Form()]):

app = FastAPI()


class Image(BaseModel):
    url: HttpUrl
    name: str


class Item(BaseModel):
    name: str
    description: Union[str, None] = None
    price: float
    tax: Union[float, None] = None
    tags: set[str] = set()
    images: Union[list[Image], None] = None


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}

@app.get("/query/optional")
def get_query_optional(query=None):
    if query is None:
        return "foo bar"
    return f"foo bar {query}"


@app.get("/query/int")
def get_query_type(query: int):
    return f"foo bar {query}"


@app.get("/query/int/optional")
def get_query_type_optional(query: Optional[int] = None):
    if query is None:
        return "foo bar"
    return f"foo bar {query}"

        {"name": "foo", "price": None, "owner_ids": None},
        {"name": "bar", "price": 1.0, "owner_ids": None},
        {"name": "baz", "price": 2.0, "owner_ids": [1, 2, 3]},

)

client = TestClient(app)


def test_function_scope() -> None:
    response = client.get("/function-scope")
    assert response.status_code == 200
    data = response.json()
    assert data["is_open"] is False


def test_request_scope() -> None:
    response = client.get("/request-scope")
    assert response.status_code == 200
    data = response.json()

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None
    tags: set[str] = set()


@app.post("/items/", response_model=Item, summary="Create an item")
async def create_item(item: Item):
    """
    Create an item with all the information:

    - **name**: each item must have a name