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

Usar `Optional[str]` en lugar de solo `str` te permitirá al editor ayudarte a detectar errores donde podrías estar asumiendo que un valor siempre es un `str`, cuando en realidad también podría ser `None`.

`Optional[Something]` es realmente un atajo para `Union[Something, None]`, son equivalentes.

Esto también significa que en Python 3.10, puedes usar `Something | None`:

        state["finally"] = True


@app.put("/invalid-user/{user_id}")
def put_invalid_user(
    user_id: str, name: str = Body(), db: dict = Depends(get_database)
):
    db[user_id] = name
    raise HTTPException(status_code=400, detail="Invalid user")


@app.put("/user/{user_id}")
def put_user(user_id: str, name: str = Body(), db: dict = Depends(get_database)):
    db[user_id] = name
    return {"message": "OK"}

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/", response_model=Item, summary="Create an item")
async def create_item(item: Item):
    """
    Create an item with all the information:

    - **name**: each item must have a name

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.post("/items/", response_model=Item, summary="Create an item")
async def create_item(item: Item):
    """
    Create an item with all the information:

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/",
    response_model=Item,
    summary="Create an item",
    description="Create an item with all the information, name, description, price, tax and a set of unique tags",
)

# Without aliases


@app.post("/required-list-str", operation_id="required_list_str")
async def read_required_list_str(p: Annotated[list[str], Body(embed=True)]):
    return {"p": p}


class BodyModelRequiredListStr(BaseModel):
    p: list[str]


@app.post("/model-required-list-str", operation_id="model_required_list_str")
def read_model_required_list_str(p: BodyModelRequiredListStr):

from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()


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

	expiryDuration time.Duration

	// Bucket to list
	bucketToList string

	// Session policy file
	sessionPolicyFile string
)

func init() {
	flag.StringVar(&stsEndpoint, "sts-ep", "http://localhost:9000", "STS endpoint")
	flag.StringVar(&ldapUsername, "u", "", "AD/LDAP Username")
	flag.StringVar(&ldapPassword, "p", "", "AD/LDAP Password")
	flag.BoolVar(&displayCreds, "d", false, "Only show generated credentials")

from typing import Annotated, Union

from fastapi import Body, FastAPI
from pydantic import BaseModel

app = FastAPI()


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


@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            openapi_examples={

		{"s.authorInfo.yearRange[0]", []any{1890.0, 1920.0, 1881.0}},
		{"s.publicationHistory[0].pages", []any{256.0, 336.0, Missing{}}},
	}
	for i, tc := range cases {
		t.Run(tc.str, func(t *testing.T) {
			jp := JSONPath{}
			err := p.ParseString(tc.str, &jp)
			// fmt.Println(jp)
			if err != nil {
				t.Fatalf("parse failed!: %d %v %s", i, err, tc)
			}

			// Read only the first json object from the file