router_b_a = APIRouter()
router_b_a_c_override = APIRouter()  # Overrides default class again


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


@app.get("/override", response_class=PlainTextResponse)
def get_path_override():
    return "Hello World"


@router_a.get("/")
def get_a():
    return {"msg": "Hello A"}


@router_a.get("/override", response_class=PlainTextResponse)

    assert response.json() == {"message": "Hello World"}
    assert (
        response.headers["access-control-allow-origin"]
        == "https://localhost.tiangolo.com"
    )

    # Test non-CORS response
    response = client.get("/")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Hello World"}

response = requests.get("http://example.com/some/url")
```

The FastAPI counterpart API *path operation* could look like:

```Python hl_lines="1"
@app.get("/some/url")
def read_url():
    return {"message": "Hello World"}
```

See the similarities in `requests.get(...)` and `@app.get(...)`.

!!! check "Inspired **FastAPI** to"
    * Have a simple and intuitive API.

from typing import Union


def say_hi(name: Union[str, None] = None):
    if name is not None:
        print(f"Hey {name}!")
    else:

from docs_src.custom_response.tutorial009c import app

client = TestClient(app)


def test_get():
    response = client.get("/")

```Python hl_lines="3"
import os

name = os.getenv("MY_NAME", "World")
print(f"Hello {name} from Python")
```

!!! tip "Tipp"
    Das zweite Argument für <a href="https://docs.python.org/3.8/library/os.html#os.getenv" class="external-link" target="_blank">`os.getenv()`</a> ist der zurückzugebende Defaultwert.

    Wenn nicht angegeben, ist er standardmäßig `None`. Hier übergeben wir `"World"` als Defaultwert.

        {"url": "https://prod.example.com", "description": "Production environment"},
    ],
    root_path="/api/v1",
)


@app.get("/app")
def read_main(request: Request):

    ],
    root_path="/api/v1",
    root_path_in_servers=False,
)


@app.get("/app")
def read_main(request: Request):

from .main import app

client = TestClient(app)


@pytest.mark.parametrize(
    "path,expected_status,expected_response",
    [
        ("/api_route", 200, {"message": "Hello World"}),
        ("/non_decorated_route", 200, {"message": "Hello World"}),
        ("/nonexistent", 404, {"detail": "Not Found"}),
    ],
)
def test_get_path(path, expected_status, expected_response):
    response = client.get(path)

```


该行显示了你的应用在本机所提供服务的 URL 地址。

### 查看

打开浏览器访问 <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a>。

你将看到如下的 JSON 响应：

```JSON
{"message": "Hello World"}
```

### 交互式 API 文档

跳转到 <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>。