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()

Раніше ми мали таку анотацію типу:

```Python
q: str | None = None
```

Тепер ми загорнемо її у `Annotated`, і отримаємо:

```Python
q: Annotated[str | None] = None
```

Обидві ці версії означають одне й те саме: `q` — це параметр, який може бути `str` або `None`, і за замовчуванням має значення `None`.

А тепер переходимо до цікавого! 🎉

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},
    "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
}

    "field (e.g. Union[Response, dict, None]) you can disable generating the "
    "response model from the type annotation with the path operation decorator "
    "parameter response_model=None. Read more: "
    "https://fastapi.tiangolo.com/tutorial/response-model/"
)


def create_model_field(
    name: str,
    type_: Any,
    default: Any | None = Undefined,
    field_info: FieldInfo | None = None,

        fun run() {
          val progressListener = object : ProgressListener {
            private var firstUpdate = true

            override fun update(bytesWritten: Long, contentLength: Long, done: Boolean) {
              if (done) {
                println("completed")
              } else {
                if (firstUpdate) {
                  firstUpdate = false
                  if (contentLength == -1L) {

	if atomic.LoadUint32(&l.done) == 0 {
		if err := f(); err != nil {
			return err
		}
		// Mark as done only when f() is successful
		atomic.StoreUint32(&l.done, 1)
	}
	return nil
}

// DoWithContext is similar to Do except that it accepts a context as an argument to be passed.
func (l *Init) DoWithContext(ctx context.Context, f func(context.Context) error) error {
	if atomic.LoadUint32(&l.done) == 0 {

			}
			err = next(resp.Msg)
			if err != nil {
				s.cancel(err)
				return err
			}
		}
	}
}

// Done will return a channel that will be closed when the stream is done.
// This mirrors context.Done().
func (s *Stream) Done() <-chan struct{} {
	return s.ctx.Done()
}

// Err will return the error that caused the stream to end.
// This mirrors context.Err().
func (s *Stream) Err() error {

在這種情況下（未使用 `Annotated`），我們必須用 `Query()` 取代函式中的預設值 `None`，因此需要用 `Query(default=None)` 來設定預設值；對 FastAPI 而言，這達到相同目的。

所以：

```Python
q: str | None = Query(default=None)
```

…會讓參數變為可選、預設值是 `None`，等同於：

```Python
q: str | None = None
```

但用 `Query` 的版本會明確宣告它是查詢參數。

接著，我們可以傳更多參數給 `Query`。此例中是用於字串的 `max_length` 參數：

```Python
q: str | None = Query(default=None, max_length=50)
```

        @app.get("/query_example/")
        def query_example(
            data: str | None = Query(
                default=None,
                example="query1",
            ),
        ):
            return data

    @app.get("/query_examples/")
    def query_examples(
        data: str | None = Query(
            default=None,
            examples=["query1", "query2"],
        ),
    ):
        return data

    "default": ...,
    "default_factory": None,
    "alias": None,
    "alias_priority": None,
    "validation_alias": None,
    "serialization_alias": None,
    "title": None,
    "field_title_generator": None,
    "description": None,
    "examples": None,
    "exclude": None,
    "exclude_if": None,
    "discriminator": None,
    "deprecated": None,
    "json_schema_extra": None,
    "frozen": None,