from contextlib import asynccontextmanager

from fastapi import FastAPI


def fake_answer_to_everything_ml_model(x: float):
    return x * 42


ml_models = {}


@asynccontextmanager
async def lifespan(app: FastAPI):
    # Load the ML model
    ml_models["answer_to_everything"] = fake_answer_to_everything_ml_model
    yield
    # Clean up the ML models and release the resources
    ml_models.clear()

def test_merged_mixed_state_lifespans() -> None:
    @asynccontextmanager
    async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
        yield

    @asynccontextmanager
    async def router_lifespan(app: FastAPI) -> AsyncGenerator[dict[str, bool], None]:
        yield {"router": True}

    @asynccontextmanager
    async def sub_router_lifespan(app: FastAPI) -> AsyncGenerator[None, None]:

from contextlib import asynccontextmanager

from fastapi import FastAPI
from fastapi.testclient import TestClient

items = {}


@asynccontextmanager
async def lifespan(app: FastAPI):
    items["foo"] = {"name": "Fighters"}
    items["bar"] = {"name": "Tenders"}
    yield
    # clean up items
    items.clear()


app = FastAPI(lifespan=lifespan)


@app.get("/items/{item_id}")
async def read_items(item_id: str):

from collections.abc import AsyncGenerator
from contextlib import AbstractContextManager
from contextlib import asynccontextmanager as asynccontextmanager
from typing import TypeVar

import anyio.to_thread
from anyio import CapacityLimiter
from starlette.concurrency import iterate_in_threadpool as iterate_in_threadpool  # noqa
from starlette.concurrency import run_in_threadpool as run_in_threadpool  # noqa
from starlette.concurrency import (  # noqa

    lenient_issubclass,
    sequence_types,
    serialize_sequence_value,
    value_is_sequence,
)
from fastapi.background import BackgroundTasks
from fastapi.concurrency import (
    asynccontextmanager,
    contextmanager_in_threadpool,
)
from fastapi.dependencies.models import Dependant
from fastapi.exceptions import DependencyScopeError
from fastapi.logger import logger

And the part after the `yield` will be executed **after** the application has finished.

### Async Context Manager { #async-context-manager }

If you check, the function is decorated with an `@asynccontextmanager`.

That converts the function into something called an "**async context manager**".

{* ../../docs_src/events/tutorial003_py310.py hl[1,13] *}

    Coroutine,
    Generator,
    Iterator,
    Mapping,
    Sequence,
)
from contextlib import (
    AbstractAsyncContextManager,
    AbstractContextManager,
    AsyncExitStack,
    asynccontextmanager,
)
from enum import Enum, IntEnum
from typing import (
    Annotated,
    Any,
    TypeVar,
    cast,
)

import anyio
from annotated_doc import Doc
from anyio.abc import ObjectReceiveStream

Cualquier función que sea válida para usar con:

* [`@contextlib.contextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager) o
* [`@contextlib.asynccontextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager)

sería válida para usar como una dependencia en **FastAPI**.

De hecho, FastAPI usa esos dos decoradores internamente.

///

Any function that is valid to use with:

* [`@contextlib.contextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager) or
* [`@contextlib.asynccontextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager)

would be valid to use as a **FastAPI** dependency.

In fact, FastAPI uses those two decorators internally.

///

///

/// note | 技術細節

任何可用於下列裝飾器的函式：

* [`@contextlib.contextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager) 或
* [`@contextlib.asynccontextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager)

都可以作為 **FastAPI** 的相依。

事實上，FastAPI 內部就是使用這兩個裝飾器。

///

## 使用 `yield` 的資料庫相依 { #a-database-dependency-with-yield }

例如，你可以用它建立一個資料庫 session，並在完成後關閉。