async def lifespan(
        app: FastAPI,
    ) -> AsyncGenerator[dict[str, str | bool], None]:
        yield {
            "app_specific": True,
            "overridden": "app",
        }

    @asynccontextmanager
    async def router_lifespan(
        app: FastAPI,
    ) -> AsyncGenerator[dict[str, str | bool], None]:
        yield {
            "router_specific": True,

```

This means that `item` could be an `int` or a `str`.

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

You can declare that a value could have a type, like `str`, but that it could also be `None`.

//// tab | Python 3.10+

```Python hl_lines="1"
{!> ../../docs_src/python_types/tutorial009_py310.py!}
```

////

}


class Token(BaseModel):
    access_token: str
    token_type: str


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


class User(BaseModel):
    username: str
    email: str | None = None
    full_name: str | None = None
    disabled: bool | None = None


class UserInDB(User):
    hashed_password: str


password_hash = PasswordHash.recommended()

from fastapi import FastAPI
from fastapi.encoders import jsonable_encoder
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str | None = None
    description: str | None = None
    price: float | None = None
    tax: float = 10.5
    tags: list[str] = []


items = {
    "foo": {"name": "Foo", "price": 50.2},
    "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},

        value: str | Missing = Missing()

    class Model(BaseModel):
        model_config = ConfigDict(
            arbitrary_types_allowed=True,
        )
        value: str | Missing = Missing()
        embedded_model: EmbeddedModel = EmbeddedModel()

    @app.post("/")
    def foo(req: Model) -> dict[str, str | None]:
        return {
            "value": req.value or None,

        self,
        *,
        flows: Annotated[
            OAuthFlowsModel | dict[str, dict[str, Any]],
            Doc(
                """
                The dictionary of OAuth2 flows.
                """
            ),
        ] = OAuthFlowsModel(),
        scheme_name: Annotated[
            str | None,
            Doc(
                """
                Security scheme name.

     *
     * @param str the string to encode
     * @param encoding the character encoding to use
     * @return encoded byte array, or empty array if str is null
     */
    public static byte[] getBytes(final String str, final Charset encoding) {
        if (str == null) {
            return new byte[0];
        }
        return str.getBytes(encoding);
    }

    /**

    # TODO: In that case, define if File() should support example/examples too
    # @app.post("/form_example")
    # def form_example(firstname: str = Form(example="John")):
    #     return firstname

    # @app.post("/form_examples")
    # def form_examples(
    #     lastname: str = Form(
    #         ...,
    #         examples={
    #             "example1": {"summary": "last name summary", "value": "Doe"},

    pass


class OtherDependencyError(Exception):
    pass


async def asyncgen_state(state: dict[str, str] = Depends(get_state)):
    state["/async"] = "asyncgen started"
    yield state["/async"]
    state["/async"] = "asyncgen completed"


def generator_state(state: dict[str, str] = Depends(get_state)):
    state["/sync"] = "generator started"
    yield state["/sync"]
    state["/sync"] = "generator completed"

                }
                System.arraycopy(str.getBytes(UNI_ENCODING), 0, dst, dstIndex, str.length() * 2);
                dstIndex += str.length() * 2;
                dst[dstIndex] = (byte) '\0';
                dstIndex++;
                dst[dstIndex++] = (byte) '\0';
            } else {
                final byte[] b = str.getBytes(OEM_ENCODING);