class User(BaseModel):
    username: str


def get_current_user(oauth_header: str | None = Security(api_key)):
    if oauth_header is None:
        return None
    user = User(username=oauth_header)
    return user


@app.get("/users/me")
def read_current_user(current_user: User | None = Depends(get_current_user)):
    if current_user is None:
        return {"msg": "Create an account first"}
    return current_user

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)
```

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()]
):

            "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
    tags: set[str] = set()


@app.post(
    "/items/",
    summary="Create an item",
    description="Create an item with all the information, name, description, price, tax and a set of unique tags",
)

from pydantic import BaseModel, Field

app = FastAPI()


class Item(BaseModel):
    name: str = Field(examples=["Foo"])
    description: str | None = Field(default=None, examples=["A very nice Item"])
    price: float = Field(examples=[35.4])
    tax: float | None = Field(default=None, examples=[3.2])


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

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: set[str] = set()


@app.post("/items/", tags=["items"])
async def create_item(item: Item) -> Item:
    return item


@app.get("/items/", tags=["items"])
async def read_items():

class ReviewNode(BaseModel):
    author: Author | None = None
    state: str


class Reviews(BaseModel):
    nodes: list[ReviewNode]


class PullRequestNode(BaseModel):
    number: int
    labels: Labels
    author: Author | None = None
    title: str
    createdAt: datetime
    lastEditedAt: datetime | None = None
    updatedAt: datetime | None = None
    state: str
    reviews: Reviews

from pydantic import BaseModel


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


app = FastAPI()


@app.post("/items/")
async def create_item(item: Item):
    item_dict = item.model_dump()
    if item.tax is not None:
        price_with_tax = item.price + item.tax
        item_dict.update({"price_with_tax": price_with_tax})

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** ✨.