from fastapi import Depends, FastAPI, HTTPException

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("We don't swallow the internal error here, we raise again 😎")
        raise


@app.get("/items/{item_id}")
def get_item(item_id: str, username: str = Depends(get_username)):
    if item_id == "portal-gun":

from typing import TYPE_CHECKING, Annotated

from fastapi import Depends, FastAPI
from fastapi.testclient import TestClient

from .utils import needs_py314

if TYPE_CHECKING:  # pragma: no cover

    class DummyUser: ...


@needs_py314
def test_stringified_annotation():
    # python3.14: Use forward reference without "from __future__ import annotations"
    async def get_current_user() -> DummyUser | None:
        return None

from fastapi import Depends, FastAPI, HTTPException

app = FastAPI()


class InternalError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except InternalError:
        print("We don't swallow the internal error here, we raise again 😎")
        raise


@app.get("/items/{item_id}")
def get_item(item_id: str, username: Annotated[str, Depends(get_username)]):

@app.get("/items/", dependencies=[Depends(verify_token), Depends(verify_key)])
async def read_items():

Although you use `Depends` in the parameters of your function the same way you use `Body`, `Query`, etc, `Depends` works a bit differently.

You only give `Depends` a single parameter.

This parameter must be something like a function.

You **don't call it** directly (don't add the parenthesis at the end), you just pass it as a parameter to `Depends()`.

And that function takes parameters in the same way that *path operation functions* do.

from typing import Annotated

from fastapi import Depends, FastAPI, HTTPException

app = FastAPI()


data = {
    "plumbus": {"description": "Freshly pickled plumbus", "owner": "Morty"},
    "portal-gun": {"description": "Gun to create portals", "owner": "Rick"},
}


class OwnerError(Exception):
    pass


def get_username():
    try:
        yield "Rick"
    except OwnerError as e:

        yield s


def broken_dep_session() -> Any:
    with acquire_session() as s:
        s.open = False
        yield s


SessionDep = Annotated[Session, Depends(dep_session)]
BrokenSessionDep = Annotated[Session, Depends(broken_dep_session)]

app = FastAPI()


@app.get("/data")
def get_data(session: SessionDep) -> Any:
    data = list(session)
    return data


@app.get("/stream-simple")

    def get_user_items(
        user_me: Annotated[dict, Depends(get_user_me)],
    ):
        call_counts["get_user_items"] += 1
        return {
            "user_items": f"user_items_{call_counts['get_user_items']}",
            "user_me": user_me,
        }

    app = FastAPI()

    @app.get("/")
    def path_operation(
        user_me: Annotated[dict, Depends(get_user_me)],

from fastapi import Depends, FastAPI
from fastapi.requests import HTTPConnection
from fastapi.testclient import TestClient
from starlette.websockets import WebSocket

app = FastAPI()
app.state.value = 42


async def extract_value_from_http_connection(conn: HTTPConnection):
    return conn.app.state.value


@app.get("/http")
async def get_value_by_http(value: int = Depends(extract_value_from_http_connection)):
    return value

/// info | Technical Details

`Security` is actually a subclass of `Depends`, and it has just one extra parameter that we'll see later.

But by using `Security` instead of `Depends`, **FastAPI** will know that it can declare security scopes, use them internally, and document the API with OpenAPI.

But when you import `Query`, `Path`, `Depends`, `Security` and others from `fastapi`, those are actually functions that return special classes.