### Always `raise` in Dependencies with `yield` and `except` { #always-raise-in-dependencies-with-yield-and-except }

If you catch an exception in a dependency with `yield`, unless you are raising another `HTTPException` or similar, you should re-raise the original exception.

You can re-raise the same exception using `raise`:

{* ../../docs_src/dependencies/tutorial008d_an_py39.py hl[17] *}

### Raise an `HTTPException` in your code { #raise-an-httpexception-in-your-code }

`HTTPException` is a normal Python exception with additional data relevant for APIs.

Because it's a Python exception, you don't `return` it, you `raise` it.

They can declare request requirements (like headers) or other sub-dependencies:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[8,13] *}

### Raise exceptions { #raise-exceptions }

These dependencies can `raise` exceptions, the same as normal dependencies:

{* ../../docs_src/dependencies/tutorial006_an_py39.py hl[10,15] *}

### Return values { #return-values }

{* ../../docs_src/websockets/tutorial002_an_py310.py hl[68:69,82] *}

/// info

As this is a WebSocket it doesn't really make sense to raise an `HTTPException`, instead we raise a `WebSocketException`.

You can use a closing code from the <a href="https://tools.ietf.org/html/rfc6455#section-7.4.1" class="external-link" target="_blank">valid codes defined in the specification</a>.

{* ../../docs_src/security/tutorial005_an_py310.py hl[47,117:129] *}

## Verify the `scopes` { #verify-the-scopes }

We now verify that all the scopes required, by this dependency and all the dependants (including *path operations*), are included in the scopes provided in the token received, otherwise raise an `HTTPException`.

Перевага використання `генерації` (raise) помилки замість `повернення` значення (return) стане більш очевидним в розділі про Залежності та Безпеку.

У цьому прикладі, якщо клієнт запитує елемент за ID, якого не існує, буде згенеровано помилку зі статус-кодом `404`:

		t.Errorf("failed to delete user, got error %v", err)
	}

	var result2 UserWithDelete
	if err := DB.Table("deleted_users").First(&result2, user.ID).Error; !errors.Is(err, gorm.ErrRecordNotFound) {
		t.Errorf("should raise record not found error, but got error %v", err)
	}

	var result3 UserWithDelete
	if err := DB.Table("deleted_users").Unscoped().First(&result3, user.ID).Error; err != nil {

        when(mockAllocInfo.getCapacity()).thenReturn(capacity);
        assertEquals(capacity, mockAllocInfo.getCapacity());
    }

    /**
     * Null pointer scenario – calls on a null reference should raise
     * {@link NullPointerException}. This test is defensive; in real code it
     * would likely be handled elsewhere.
     */
    @Test
    @DisplayName("calling getters on null reference throws NPE")

あなた（または使用しているライブラリ）が`raise`するかもしれないカスタム例外`UnicornException`があるとしましょう。

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:

{* ../../docs_src/handling_errors/tutorial003.py hl[5,6,7,13,14,15,16,17,18,24] *}

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。

    }

    @Test
    void throwsOnUnexpectedStructureSize() throws Exception {
        // structureSize != 49 and != 9 should raise an exception
        byte[] header = buildHeader(NtStatus.NT_STATUS_SUCCESS);
        byte[] buf = new byte[header.length + 10];
        System.arraycopy(header, 0, buf, 0, header.length);