# Concurrency and async / await { #concurrency-and-async-await }

Details about the `async def` syntax for *path operation functions* and some background about asynchronous code, concurrency, and parallelism.

## In a hurry? { #in-a-hurry }

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

If you are using third party libraries that tell you to call them with `await`, like:

```Python
results = await some_library()
```

    public void test_constructorWithMessageAndCause() {
        // Test constructor with message and cause
        String message = "Query parsing failed";
        Exception cause = new IllegalArgumentException("Invalid query syntax");

        SearchQueryException exception = new SearchQueryException(message, cause);

        assertEquals(message, exception.getMessage());
        assertEquals(cause, exception.getCause());

    }

    /**
     * Append formatted content to the buffer.
     * @see String#format(String, Object...)
     *
     * @param pattern a <a href="../util/Formatter.html#syntax">format string</a>
     * @param args arguments referenced by the format specifiers in the format string
     * @return the current builder
     */
    @Nonnull

Se você quiser declarar o parâmetro de consulta `q` sem um `Query` nem um valor padrão, e o parâmetro de rota `item_id` usando `Path`, e definí-los em uma ordem diferente, Python tem um pequeno truque na sintaxe para isso.

Passe `*`, como o primeiro parâmetro da função.

* declare the `q` query parameter without a `Query` nor any default value
* declare the path parameter `item_id` using `Path`
* have them in a different order
* not use `Annotated`

...Python has a little special syntax for that.

Pass `*`, as the first parameter of the function.

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Nur modernes Python

Alles basiert auf **Python 3.8 Typ**-Deklarationen (dank Pydantic). Es muss keine neue Syntax gelernt werden, nur standardisiertes modernes Python.

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Just Modern Python { #just-modern-python }

It's all based on standard **Python type** declarations (thanks to Pydantic). No new syntax to learn. Just standard modern Python.

If you need a 2 minute refresher of how to use Python types (even if you don't use FastAPI), check the short tutorial: [Python Types](python-types.md){.internal-link target=_blank}.

```

dann ist das ein „Callable“ (ein „Aufrufbares“).

## Klassen als Abhängigkeiten

Möglicherweise stellen Sie fest, dass Sie zum Erstellen einer Instanz einer Python-Klasse die gleiche Syntax verwenden.

Zum Beispiel:

```Python
class Cat:
    def __init__(self, name: str):
        self.name = name


fluffy = Cat(name="Mr Fluffy")
```

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Apenas Python moderno

Tudo é baseado no padrão das declarações de **tipos do Python 3.8** (graças ao Pydantic). Nenhuma sintaxe nova para aprender. Apenas o padrão moderno do Python.

     * constructor's. This is an arbitrary rule since no existing language spec mandates one way or
     * the other. From the declaration syntax, the class type parameter appears first, but the call
     * syntax may show up in opposite order such as {@code new <A>Foo<B>()}.
     */
    @Override
    public final TypeVariable<?>[] getTypeParameters() {