from pydantic_settings import BaseSettings


class Settings(BaseSettings):
    app_name: str = "Awesome API"
    admin_email: str

from typing import Annotated


def say_hello(name: Annotated[str, "this is just metadata"]) -> str:

from fastapi import APIRouter, FastAPI
from pydantic import BaseModel, HttpUrl

app = FastAPI()


class Invoice(BaseModel):
    id: str
    title: Union[str, None] = None
    customer: str
    total: float


class InvoiceEvent(BaseModel):
    description: str
    paid: bool


class InvoiceEventReceived(BaseModel):
    ok: bool


invoices_callback_router = APIRouter()

        SmbComNTCreateAndX req = createRequest(0, 0);
        String str = req.toString();
        assertTrue(str.startsWith("SmbComNTCreateAndX["), "toString should start with class name");
        assertTrue(str.contains("name=test.txt"), "The file name should appear");
        // securityFlags are set to 0x03 – verify hex sequence
        assertTrue(str.contains("securityFlags=0x03"), "securityFlags should be present");
    }

In this example, it would convert the Pydantic model to a `dict`, and the `datetime` to a `str`.

The result of calling it is something that can be encoded with the Python standard <a href="https://docs.python.org/3/library/json.html#json.dumps" class="external-link" target="_blank">`json.dumps()`</a>.

    void testToString() {
        smb.command = ServerMessageBlock.SMB_COM_ECHO;
        smb.errorCode = 0;
        smb.mid = 1;
        String str = smb.toString();
        assertTrue(str.contains("command=SMB_COM_ECHO"));
        assertTrue(str.contains("errorCode=0"));
        assertTrue(str.contains("mid=1"));
    }

    @Test
    void testToStringUnknownCommand() {
        smb.command = (byte) 0xFF; // Unknown command

#### `Optional`

`str`과 같이 타입을 선언할 때 `Optional`을 쓸 수도 있는데, "선택적(Optional)"이기때문에 `None`도 될 수 있습니다:

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

`Optional[str]`을 `str` 대신 쓰게 되면, 특정 값이 실제로는 `None`이 될 수도 있는데 항상 `str`이라고 가정하는 상황에서 에디터가 에러를 찾게 도와줄 수 있습니다.

#### Generic(제네릭) 타입

이 타입은 대괄호 안에 매개변수를 가지며, 종류는:

* `List`
* `Tuple`
* `Set`
* `Dict`

class MessageEventType(str, Enum):
    alpha = "alpha"
    beta = "beta"


class MessageEvent(BaseModel):
    event_type: MessageEventType = Field(default=MessageEventType.alpha)
    output: str


class MessageOutput(BaseModel):
    body: str = ""
    events: list[MessageEvent] = []


class Message(BaseModel):
    input: str
    output: MessageOutput

        You can't see this part of the docstring, it's private!
        """

        line_1: str
        city: str
        state_province: str

    class Facility(BaseModel):
        id: str
        address: Address

    app = FastAPI()

    @app.get("/facilities/{facility_id}")
    def get_facility(facility_id: str) -> Facility:
        return Facility(
            id=facility_id,

def get_username():
    try:
        yield "Rick"
    except OwnerError as e:
        raise HTTPException(status_code=400, detail=f"Owner error: {e}")


@app.get("/items/{item_id}")
def get_item(item_id: str, username: str = Depends(get_username)):
    if item_id not in data:
        raise HTTPException(status_code=404, detail="Item not found")
    item = data[item_id]
    if item["owner"] != username:
        raise OwnerError(username)