from fastapi import Cookie, Depends, FastAPI

app = FastAPI()


def query_extractor(q: str | None = None):
    return q


def query_or_cookie_extractor(
    q: str = Depends(query_extractor), last_query: str | None = Cookie(default=None)
):
    if not q:
        return last_query
    return q


@app.get("/items/")
async def read_query(query_or_default: str = Depends(query_or_cookie_extractor)):

]


class Author(BaseModel):
    login: str
    avatarUrl: str | None = None
    url: str | None = None


class CommentsNode(BaseModel):
    createdAt: datetime
    author: Author | None = None
    minimizedReason: LowerStr | None = None


class Replies(BaseModel):
    totalCount: int
    nodes: list[CommentsNode]

        "required": ["p"],
        "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: dict | None):
    client = TestClient(app)
    response = client.post(path, json=json)
    assert response.status_code == 422

from typing import Annotated

from fastapi import Cookie, Depends, FastAPI

app = FastAPI()


def query_extractor(q: str | None = None):
    return q


def query_or_cookie_extractor(
    q: Annotated[str, Depends(query_extractor)],
    last_query: Annotated[str | None, Cookie()] = None,
):
    if not q:
        return last_query
    return q


@app.get("/items/")
async def read_query(

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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


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


@app.get("/items/")
async def read_items() -> list[Item]:
    return [

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


class Item(BaseModel):
    name: str
    description: str | None = None
    price: float
    tax: float | None = None

    model_config = {
        "json_schema_extra": {
            "examples": [
                {
                    "name": "Foo",
                    "description": "A very nice Item",
                    "price": 35.4,

例えば、`str` または `None` になり得ることを宣言できます:

```python
from typing import Union


def say_hi(name: Union[str, None]):
        print(f"Hi {name}!")
```

`typing` には、`None` を取り得ることを宣言するための短縮形として `Optional` もあります。

ここからは私のとても主観的な提案です:

- 🚨 `Optional[SomeType]` の使用は避けましょう
- 代わりに ✨ **`Union[SomeType, None]` を使いましょう** ✨。

app = FastAPI()


@app.post("/files/")
async def create_file(file: Annotated[bytes | None, File()] = None):
    if not file:
        return {"message": "No file sent"}
    else:
        return {"file_size": len(file)}


@app.post("/uploadfile/")
async def create_upload_file(file: UploadFile | None = None):
    if not file:
        return {"message": "No upload file sent"}
    else:

```Python
say_hi(name=None)  # Це працює, None припустимий 🎉
```

Гарна новина: у більшості випадків ви зможете просто використовувати `|`, щоб визначати об'єднання типів:

```python
def say_hi(name: str | None):
    print(f"Hey {name}!")
```

type lazyInit struct {
	done uint32
	m    sync.Mutex
}

func (l *lazyInit) Do(f func() error) error {
	if atomic.LoadUint32(&l.done) == 0 {
		return l.doSlow(f)
	}
	return nil
}

func (l *lazyInit) doSlow(f func() error) error {
	l.m.Lock()
	defer l.m.Unlock()
	if atomic.LoadUint32(&l.done) == 0 {
		if err := f(); err != nil {
			return err
		}