### 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.

    user = fake_decode_token(token)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Not authenticated",
            headers={"WWW-Authenticate": "Bearer"},
        )
    return user


async def get_current_active_user(current_user: User = Depends(get_current_user)):
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")

            if self.auto_error:
                raise self.make_not_authenticated_error()
            else:
                return None
        try:
            data = b64decode(param).decode("ascii")
        except (ValueError, UnicodeDecodeError, binascii.Error) as e:
            raise self.make_not_authenticated_error() from e
        username, separator, password = data.partition(":")

`yield`を持つ依存関係で`except`を使って例外をキャッチし、それを再度raiseしない（または新しい例外をraiseしない）場合、通常のPythonと同じように、FastAPIは例外があったことに気づけません:

{* ../../docs_src/dependencies/tutorial008c_an_py310.py hl[15:16] *}

この場合、（`HTTPException`やそれに類するものをraiseしていないため）クライアントには適切に*HTTP 500 Internal Server Error*レスポンスが返りますが、サーバーには**ログが一切残らず**、何がエラーだったのかを示す他の手がかりもありません。 😱

### `yield`と`except`を持つ依存関係では常に`raise`する { #always-raise-in-dependencies-with-yield-and-except }

    Syntax of comments depends on the language of the code block.
    Raises ValueError if the blocks are not compatible (different languages or different number of lines).
    """

    start_line = block_a["start_line_no"]
    end_line_no = start_line + len(block_a["content"]) - 1

    if block_a["lang"] != block_b["lang"]:
        raise ValueError(
            f"Code block (lines {start_line}-{end_line_no}) "

    hero = session.get(Hero, hero_id)
    if not hero:
        raise HTTPException(status_code=404, detail="Hero not found")
    return hero


@app.patch("/heroes/{hero_id}", response_model=HeroPublic)
def update_hero(hero_id: int, hero: HeroUpdate, session: SessionDep):
    hero_db = session.get(Hero, hero_id)
    if not hero_db:
        raise HTTPException(status_code=404, detail="Hero not found")

    Note over client,operation: Can raise exceptions, including HTTPException
    client ->> dep: Start request
    Note over dep: Run code up to yield
    opt raise Exception
        dep -->> handler: Raise Exception
        handler -->> client: HTTP error response
    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> dep: Raise Exception (e.g. HTTPException)
        opt handle

	user := User{Name: "transaction"}
	if err := tx.Save(&user).Error; err != nil {
		t.Fatalf("No error should raise")
	}

	if err := tx.Commit().Error; err != nil {
		t.Fatalf("Commit should not raise error")
	}

	if err := tx.Rollback().Error; err == nil {
		t.Fatalf("Rollback after commit should raise error")
	}
}

func TestTransactionWithSavePoint(t *testing.T) {
	tx := DB.Begin()

        fake_database.update(temp_database)
    except HTTPException:
        state["except"] = True
        raise
    finally:
        state["finally"] = True


@app.put("/invalid-user/{user_id}")
def put_invalid_user(
    user_id: str, name: str = Body(), db: dict = Depends(get_database)
):
    db[user_id] = name
    raise HTTPException(status_code=400, detail="Invalid user")


@app.put("/user/{user_id}")

app = FastAPI()


async def verify_token(x_token: Annotated[str, Header()]):
    if x_token != "fake-super-secret-token":
        raise HTTPException(status_code=400, detail="X-Token header invalid")


async def verify_key(x_key: Annotated[str, Header()]):
    if x_key != "fake-super-secret-key":
        raise HTTPException(status_code=400, detail="X-Key header invalid")
    return x_key