Callable<T> callable, ListeningExecutorService listeningExecutorService) {
    checkNotNull(callable);
    checkNotNull(listeningExecutorService);
    return () -> listeningExecutorService.submit(callable);
  }

  /**
   * Wraps the given callable such that for the duration of {@link Callable#call} the thread that is
   * running will have the given name.
   *
   * @param callable The callable to wrap

        };

    results.add(serializer.submit(Callables.returning(null), manualExecutor));
    Future<?>[] thingToCancel = new Future<?>[1];
    results.add(
        serializer.submit(
            () -> {
              thingToCancel[0].cancel(false);
              return null;
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());

  public void testReturning() throws Exception {
    assertThat(Callables.returning(null).call()).isNull();

    Object value = new Object();
    Callable<Object> callable = Callables.returning(value);
    assertThat(callable.call()).isEqualTo(value);
    // Expect the same value on subsequent calls
    assertThat(callable.call()).isEqualTo(value);
  }

  @J2ktIncompatible
  @GwtIncompatible

  public void testReturning() throws Exception {
    assertThat(Callables.returning(null).call()).isNull();

    Object value = new Object();
    Callable<Object> callable = Callables.returning(value);
    assertThat(callable.call()).isEqualTo(value);
    // Expect the same value on subsequent calls
    assertThat(callable.call()).isEqualTo(value);
  }

  @J2ktIncompatible
  @GwtIncompatible

    }
  }

  private static List<Callable<String>> createTasks(int n) {
    List<Callable<String>> callables = new ArrayList<>();
    for (int i = 0; i < n; i++) {
      callables.add(Callables.returning(RESULT_VALUE + i));
    }
    return callables;
  }

  private static final class WrappedCallable<T> implements Callable<T> {
    private final Callable<T> delegate;

    }
  }

  private static List<Callable<String>> createTasks(int n) {
    List<Callable<String>> callables = new ArrayList<>();
    for (int i = 0; i < n; i++) {
      callables.add(Callables.returning(RESULT_VALUE + i));
    }
    return callables;
  }

  private static final class WrappedCallable<T> implements Callable<T> {
    private final Callable<T> delegate;

        };

    results.add(serializer.submit(Callables.returning(null), manualExecutor));
    Future<?>[] thingToCancel = new Future<?>[1];
    results.add(
        serializer.submit(
            () -> {
              thingToCancel[0].cancel(false);
              return null;
            },
            directExecutor()));
    thingToCancel[0] = serializer.submit(Callables.returning(null), directExecutor());

    List<Callable<T>> tasks = ImmutableList.of();
    List<? extends Future<?>> unused = executor.invokeAll(tasks);
  }

  public void testListeningDecorator() throws Exception {
    ListeningExecutorService service = listeningDecorator(newDirectExecutorService());
    assertThat(listeningDecorator(service)).isSameInstanceAs(service);
    List<Callable<String>> callables = ImmutableList.of(Callables.returning("x"));

    List<Callable<T>> tasks = ImmutableList.of();
    List<? extends Future<?>> unused = executor.invokeAll(tasks);
  }

  public void testListeningDecorator() throws Exception {
    ListeningExecutorService service = listeningDecorator(newDirectExecutorService());
    assertThat(listeningDecorator(service)).isSameInstanceAs(service);
    List<Callable<String>> callables = ImmutableList.of(Callables.returning("x"));

So, a Python class is also a **callable**.

Then, in **FastAPI**, you could use a Python class as a dependency.

What FastAPI actually checks is that it is a "callable" (function, class or anything else) and the parameters defined.