Це звичайна функція, яка може отримувати параметри.

Вона може бути асинхронною `async def` або звичайною `def` функцією – **FastAPI** обробить її правильно.

У нашому випадку функція записує у файл (імітуючи надсилання email).

І оскільки операція запису не використовує `async` та `await`, ми визначаємо функцію як звичайну `def`:

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## Додавання фонової задачі

from fastapi.testclient import TestClient

from docs_src.handling_errors.tutorial001_py39 import app

client = TestClient(app)


def test_get_item():
    response = client.get("/items/foo")
    assert response.status_code == 200, response.text
    assert response.json() == {"item": "The Foo Wrestlers"}


def test_get_item_not_found():
    response = client.get("/items/bar")
    assert response.status_code == 404, response.text

from docs_src.path_params.tutorial004_py39 import app

client = TestClient(app)


def test_file_path():
    response = client.get("/files/home/johndoe/myfile.txt")
    print(response.content)
    assert response.status_code == 200, response.text
    assert response.json() == {"file_path": "home/johndoe/myfile.txt"}


def test_root_file_path():
    response = client.get("/files//home/johndoe/myfile.txt")

from fastapi import FastAPI
from fastapi.testclient import TestClient
from inline_snapshot import snapshot
from pydantic import BaseModel, Field
from typing_extensions import Literal


def test_discriminator_pydantic_v2() -> None:
    from pydantic import Tag

    app = FastAPI()

    class FirstItem(BaseModel):
        value: Literal["first"]
        price: int

    class OtherItem(BaseModel):

async def dep0(response: Response):
    response.headers["x-level0"] = "True"


async def dep1(response: Response):
    response.headers["x-level1"] = "True"


async def dep2(response: Response):
    response.headers["x-level2"] = "True"


async def dep3(response: Response):
    response.headers["x-level3"] = "True"


async def dep4(response: Response):

                "in": "query",
            },
        ]
    },
)
def route_with_extra_query_parameters(standard_query_param: Optional[int] = 50):
    return {}


client = TestClient(app)


def test_get_route():
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert response.json() == {}


def test_openapi():
    response = client.get("/openapi.json")

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>或者使用 <code>async def</code>...</summary>

如果你的代码里会出现 `async` / `await`，请使用 `async def`：

```Python hl_lines="9  14"
from typing import Union

    assertThat(response1.body.source().readUtf8(3)).isEqualTo("ABC")
    assertThat(response2.body.source().readUtf8(3)).isEqualTo("GHI")
    assertThat(response1.body.source().readUtf8(3)).isEqualTo("DEF")
    assertThat(response2.body.source().readUtf8(3)).isEqualTo("JKL")
    val c0e0 = server.takeRequest()
    assertThat(c0e0.connectionIndex).isEqualTo(0)
    assertThat(c0e0.exchangeIndex).isEqualTo(0)

This is necessary on Windows, because some applications do not understand/handle
Linux-like paths MSYS uses, for example, Docker.
"""

import argparse
import os


def should_convert(var_name: str,
                   blacklist: list[str] | None,
                   whitelist_prefix: list[str] | None):
  """Check the variable name against white/black lists."""

It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001_py39.py hl[6:9] *}