from typing import Union

from pydantic.v1 import BaseModel


class Item(BaseModel):
    name: str
    description: Union[str, None] = None

from dataclasses import field  # (1)

from fastapi import FastAPI
from pydantic.dataclasses import dataclass  # (2)


@dataclass
class Item:
    name: str
    description: str | None = None


@dataclass
class Author:
    name: str
    items: list[Item] = field(default_factory=list)  # (3)


app = FastAPI()


@app.post("/authors/{author_id}/items/", response_model=Author)  # (4)

from dataclasses import field  # (1)
from typing import Union

from fastapi import FastAPI
from pydantic.dataclasses import dataclass  # (2)


@dataclass
class Item:
    name: str
    description: Union[str, None] = None


@dataclass
class Author:
    name: str
    items: list[Item] = field(default_factory=list)  # (3)


app = FastAPI()


@app.post("/authors/{author_id}/items/", response_model=Author)  # (4)

        "title": body_model_name,
        "type": "object",
    }


@pytest.mark.parametrize("json", [None, {}])
@pytest.mark.parametrize(
    "path",
    ["/required-list-str", "/model-required-list-str"],
)
def test_required_list_str_missing(path: str, json: Union[dict, None]):
    client = TestClient(app)
    response = client.post(path, json=json)
    assert response.status_code == 422

app = FastAPI()


class Item(BaseModel):
    name: str
    price: float
    is_offer: Union[bool, None] = None


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}


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

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_item(item_id: str, q: str | None = None):
    if q:
        return {"item_id": item_id, "q": q}

from typing import Union

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(x_token: Union[list[str], None] = Header(default=None)):

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[list[str], None], Query()] = None):
    query_items = {"q": q}

    if oauth_header is None:
        return None
    user = User(username=oauth_header)
    return user


@app.post("/login")
def login(form_data: OAuth2PasswordRequestFormStrict = Depends()):
    return form_data


@app.get("/users/me")
def read_users_me(current_user: Optional[User] = Depends(get_current_user)):
    if current_user is None:
        return {"msg": "Create an account first"}

```

////

Em ambos os casos, isso significa que `item` poderia ser um `int` ou um `str`.

#### Possivelmente `None` { #possibly-none }

Você pode declarar que um valor pode ter um tipo, como `str`, mas que ele também pode ser `None`.

No Python 3.6 e superior (incluindo o Python 3.10) você pode declará-lo importando e utilizando `Optional` do módulo `typing`.

```Python hl_lines="1  4"