assert response.json() == {
        "detail": [
            {
                "type": "missing",
                "loc": ["query", "p"],
                "msg": "Field required",
                "input": IsOneOf(None, {}),
            }
        ]
    }


@pytest.mark.parametrize(
    "path",
    ["/required-list-str", "/model-required-list-str"],
)
def test_required_list_str(path: str):
    client = TestClient(app)

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    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": []},
}

* der Inhalt, den Ihr Programm dem System übergeben hat, auf die Festplatte geschrieben wurde
* eine Remote-API-Operation beendet wurde
* Eine Datenbankoperation abgeschlossen wurde
* eine Datenbankabfrage die Ergebnisse zurückgegeben hat
* usw.

```

/// tip | 팁

<a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> 의 두 번째 인자는 반환할 기본값입니다.

여기서는 `"World"`를 넣었기에 기본값으로써 사용됩니다. 넣지 않으면 `None` 이 기본값으로 사용됩니다.

///

그러면 해당 파이썬 프로그램을 다음과 같이 호출할 수 있습니다:

//// tab | Linux, macOS, Windows Bash

<div class="termy">

```console
// Here we don't set the env var yet
$ python main.py

from typing import Optional


def say_hi(name: Optional[str] = None):
    if name is not None:
        print(f"Hey {name}!")
    else:

from fastapi import FastAPI, Header

app = FastAPI()


@app.get("/items/")
async def read_items(
    strange_header: str | None = Header(default=None, convert_underscores=False),
):

def test_union_body_discriminator_assignment(client: TestClient) -> None:
    response = client.post("/pet/assignment", json={"pet_type": "cat", "meows": 5})
    assert response.status_code == 200, response.text
    assert response.json() == {"pet_type": "cat", "meows": 5}


def test_union_body_discriminator_annotated(client: TestClient) -> None:
    response = client.post("/pet/annotated", json={"pet_type": "dog", "barks": 3.5})

```

////

В обоих случаях это означает, что `item` может быть `int` или `str`.

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

Вы можете объявить, что значение может иметь определённый тип, например `str`, но также может быть и `None`.

В Python 3.6 и выше (включая Python 3.10) это можно объявить, импортировав и используя `Optional` из модуля `typing`.

```Python hl_lines="1  4"

	var files []string
	for _, line := range lines {
		if len(line) == 0 {
			continue
		}
		xmlLines := getLines(parseMobileProvision(string(line)))
		matches := 0
		for _, udid := range udids {
			for _, xmlLine := range xmlLines {
				if bytes.Contains(xmlLine, udid) {
					matches++
				}
			}
		}
		if matches == len(udids) {
			files = append(files, string(line))
		}
	}
	return files
}

from typing import Annotated

from fastapi import Cookie, FastAPI

app = FastAPI()


@app.get("/items/")
async def read_items(ads_id: Annotated[str | None, Cookie()] = None):