PacDataInputStream pdis = createInputStream(data);
        PacUnicodeString str = pdis.readUnicodeString();
        assertEquals(4, str.getLength());
        assertEquals(4, str.getMaxLength());
        assertEquals(0x1234, str.getPointer());
    }

    @Test
    public void testReadUnicodeStringMalformed() throws IOException {
        // length > maxLength

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/{item_id}")
async def read_user_item(
    item_id: str, needy: str, skip: int = 0, limit: int | None = None
):
    item = {"item_id": item_id, "needy": needy, "skip": skip, "limit": limit}

        class Item(BaseModel):
            title: str

        @app.get("/items/")
        def read_items(q: dict[str, Item] = Query(default=None)):
            pass  # pragma: no cover


def test_invalid_simple_dict():
    with pytest.raises(AssertionError):
        app = FastAPI()

        class Item(BaseModel):
            title: str

        @app.get("/items/")

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009_py39.py!}
```

Использование `Optional[str]` вместо просто `str` позволит редактору кода помочь вам обнаружить ошибки, когда вы предполагаете, что значение всегда `str`, хотя на самом деле оно может быть и `None`.

`Optional[Something]` — это на самом деле сокращение для `Union[Something, None]`, они эквивалентны.

from pydantic import BaseModel, SecretStr
from pydantic_settings import BaseSettings


class Settings(BaseSettings):
    github_repository: str
    github_token: SecretStr


class Repo(BaseModel):
    name: str
    html_url: str
    stars: int
    owner_login: str
    owner_html_url: str


def main() -> None:
    logging.basicConfig(level=logging.INFO)
    settings = Settings()

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel


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


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):

from typing import Annotated

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: str | None = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q

from typing import Union

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: Union[str, None] = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q

from fastapi import FastAPI
from fastapi.responses import JSONResponse
from pydantic import BaseModel


class Item(BaseModel):
    id: str
    value: str


class Message(BaseModel):
    message: str


app = FastAPI()


@app.get(
    "/items/{item_id}",
    response_model=Item,
    responses={
        404: {"model": Message, "description": "The item was not found"},
        200: {

def get_openapi(
    *,
    title: str,
    version: str,
    openapi_version: str = "3.1.0",
    summary: Optional[str] = None,
    description: Optional[str] = None,
    routes: Sequence[BaseRoute],
    webhooks: Optional[Sequence[BaseRoute]] = None,
    tags: Optional[list[dict[str, Any]]] = None,
    servers: Optional[list[dict[str, Union[str, Any]]]] = None,
    terms_of_service: Optional[str] = None,