```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Internamente, `open("./somefile.txt")` crea un objeto llamado "Context Manager".

Cuando el bloque `with` termina, se asegura de cerrar el archivo, incluso si hubo excepciones.

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Под капотом вызов `open("./somefile.txt")` создаёт объект, называемый «контекстным менеджером».

Когда блок `with` завершается, он обязательно закрывает файл, даже если были исключения.

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Im Hintergrund erstellt das `open("./somefile.txt")` ein Objekt, das als „Kontextmanager“ bezeichnet wird.

/// tip

You can use `async` or regular functions.

**FastAPI** will do the right thing with each, the same as with normal dependencies.

///

## A dependency with `yield` and `try` { #a-dependency-with-yield-and-try }

If you use a `try` block in a dependency with `yield`, you'll receive any exception that was thrown when using the dependency.

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Por baixo dos panos, o código `open("./somefile.txt")` cria um objeto que é chamado de "Gerenciador de Contexto".

Quando o bloco `with` finaliza, ele se certifica de fechar o arquivo, mesmo que tenha ocorrido alguma exceção.

        uses: actions/setup-java@v5
        with:
          distribution: 'zulu'
          java-version: 8.0.242

      - name: Configure JDK
        uses: actions/setup-java@v5
        with:
          distribution: 'zulu'
          java-version: 11

      - name: Configure JDK
        uses: actions/setup-java@v5
        with:
          distribution: 'zulu'
          java-version: 17

You can read more about it in the docs for [Dependencies with `yield` - Early exit and `scope`](../tutorial/dependencies/dependencies-with-yield.md#early-exit-and-scope).

### Dependencies with `yield` and `StreamingResponse`, Technical Details { #dependencies-with-yield-and-streamingresponse-technical-details }

<img src="/img/tutorial/security/image11.png">

## JWT token with scopes { #jwt-token-with-scopes }

Now, modify the token *path operation* to return the scopes requested.

We are still using the same `OAuth2PasswordRequestForm`. It includes a property `scopes` with a `list` of `str`, with each scope it received in the request.

		return 1, data[0:1], nil
	}

	// Fast path 2: Correct UTF-8 decode without error.
	_, width := utf8.DecodeRune(data)
	if width > 1 {
		// It's a valid encoding. Width cannot be one for a correctly encoded
		// non-ASCII rune.
		return width, data[0:width], nil
	}

	// We know it's an error: we have width==1 and implicitly r==utf8.RuneError.
	// Is the error because there wasn't a full rune to be decoded?

But at the same time, functions defined with `async def` have to be "awaited". So, functions with `async def` can only be called inside of functions defined with `async def` too.

So, about the egg and the chicken, how do you call the first `async` function?