type: SchemaType | list[SchemaType] | None = None
    enum: list[Any] | None = None
    const: Any | None = None
    multipleOf: float | None = Field(default=None, gt=0)
    maximum: float | None = None
    exclusiveMaximum: float | None = None
    minimum: float | None = None
    exclusiveMinimum: float | None = None
    maxLength: int | None = Field(default=None, ge=0)
    minLength: int | None = Field(default=None, ge=0)

We had this type annotation:

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

What we will do is wrap that with `Annotated`, so it becomes:

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

Both of those versions mean the same thing, `q` is a parameter that can be a `str` or `None`, and by default, it is `None`.

Now let's jump to the fun stuff. 🎉

예를 들어, 어떤 값이 `str` 또는 `None`이 될 수 있다고 선언할 수 있습니다:

```python
from typing import Union


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

`typing`에는 `None`이 될 수 있음을 선언하는 축약형으로 `Optional`도 있습니다.

아주 개인적인 관점에서의 팁입니다:

- 🚨 `Optional[SomeType]` 사용은 피하세요
- 대신 ✨ **`Union[SomeType, None]`를 사용하세요** ✨.

            """
        ),
    ] = None
    event: Annotated[
        str | None,
        Doc(
            """
            Optional event type name.

            Maps to `addEventListener(event, ...)` on the browser. When omitted,
            the browser dispatches on the generic `message` event.
            """
        ),
    ] = None
    id: Annotated[
        str | None,
        AfterValidator(_check_id_no_null),

      "gridPos": {
        "h": 6,
        "w": 3,
        "x": 0,
        "y": 0
      },
      "id": 1,
      "maxDataPoints": 100,
      "options": {
        "colorMode": "value",
        "graphMode": "none",
        "justifyMode": "auto",
        "orientation": "auto",
        "reduceOptions": {
          "calcs": [
            "mean"
          ],
          "fields": "",
          "values": false
        },

            "axisLabel": "",
            "axisPlacement": "auto",
            "barAlignment": 0,
            "drawStyle": "line",
            "fillOpacity": 10,
            "gradientMode": "none",
            "hideFrom": {
              "legend": false,
              "tooltip": false,
              "viz": false
            },
            "insertNulls": false,
            "lineInterpolation": "linear",

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


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


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item, user: User):

app = FastAPI()


class Image(BaseModel):
    url: HttpUrl
    name: str


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


@app.put("/items/{item_id}")
async def update_item(item_id: int, item: Item):
    results = {"item_id": item_id, "item": item}

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


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


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


@app.put("/items/{item_id}")
async def update_item(
    item_id: int, item: Item, user: User, importance: Annotated[int, Body()]
):

from pydantic import BaseModel, Field
from starlette.testclient import TestClient

app = FastAPI()


class Item(BaseModel):
    name: str = Field(alias="aliased_name")
    price: float | None = None
    owner_ids: list[int] | None = None


@app.get("/items/valid", response_model=Item)
def get_valid():
    return Item(aliased_name="valid", price=1.0)


@app.get("/items/coerce", response_model=Item)
def get_coerce():