* the contents your program gave to the system to be written to disk
* a remote API operation
* a database operation to finish
* a database query to return the results
* etc.

As the execution time is consumed mostly by waiting for <abbr title="Input and Output">I/O</abbr> operations, they call them "I/O bound" operations.

そして、この例外をFastAPIでグローバルに処理したいと思います。

カスタム例外ハンドラを`@app.exception_handler()`で追加することができます:

```Python hl_lines="5 6 7  13 14 15 16 17 18  24"
{!../../../docs_src/handling_errors/tutorial003.py!}
```

ここで、`/unicorns/yolo`をリクエストすると、*path operation*は`UnicornException`を`raise`します。

しかし、これは`unicorn_exception_handler`で処理されます。

そのため、HTTPステータスコードが`418`で、JSONの内容が以下のような明確なエラーを受け取ることになります:

```JSON

                    "type": "type_error.dict",
                }
            ]
        }
    )


@needs_py310
def test_other_exceptions(client: TestClient):
    with patch("json.loads", side_effect=Exception):
        response = client.post("/items/", json={"test": "test2"})
        assert response.status_code == 400, response.text


@needs_py310
def test_openapi_schema(client: TestClient):

                    "type": "type_error.dict",
                }
            ]
        }
    )


def test_other_exceptions(client: TestClient):
    with patch("json.loads", side_effect=Exception):
        response = client.post("/items/", json={"test": "test2"})
        assert response.status_code == 400, response.text


def test_openapi_schema(client: TestClient):

## Dependencies with `yield` and `except`

If you catch an exception using `except` in a dependency with `yield` and you don't raise it again (or raise a new exception), FastAPI won't be able to notice there was an exception, the same way that would happen with regular Python:

* une opération effectuée à distance par une API se termine
* une opération en BDD se termine
* une requête à une BDD renvoie un résultat
* etc.

    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> dep: Raise other exception
    end
    Note over dep: After yield
    opt Handle other exception
        dep -->> dep: Handle exception, can't change response. E.g. close DB session.
    end
```

!!! info "情報"

```Python hl_lines="5-7  13-18  24"
{!../../../docs_src/handling_errors/tutorial003.py!}
```

Nesse cenário, se você fizer uma requisição para `/unicorns/yolo`, a *operação de caminho* vai lançar (`raise`) o `UnicornException`.

Essa exceção será manipulada, contudo, pelo `unicorn_exception_handler`.

Wir erstellen eine `HTTPException`, die wir später an mehreren Stellen wiederverwenden (`raise`n) können.

In diese Exception fügen wir (falls vorhanden) die erforderlichen Scopes als durch Leerzeichen getrennten String ein (unter Verwendung von `scope_str`). Wir fügen diesen String mit den Scopes in den Header `WWW-Authenticate` ein (das ist Teil der Spezifikation).

With the Dependency Injection system, you can also tell **FastAPI** that your *path operation function* also "depends" on something else that should be executed before your *path operation function*, and **FastAPI** will take care of executing it and "injecting" the results.

Other common terms for this same idea of "dependency injection" are:

* resources
* providers
* services
* injectables
* components

## **FastAPI** plug-ins