## First Steps

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable"

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

{* ../../docs_src/dependencies/tutorial001_an_py310.py hl[8:9] *}

## Dependency Injection

Using `BackgroundTasks` also works with the dependency injection system, you can declare a parameter of type `BackgroundTasks` at multiple levels: in a *path operation function*, in a dependency (dependable), in a sub-dependency, etc.

**FastAPI** knows what to do in each case and how to reuse the same object, so that all the background tasks are merged together and are run in the background afterwards:

        **extra,
    )


def Depends(  # noqa: N802
    dependency: Annotated[
        Optional[Callable[..., Any]],
        Doc(
            """
            A "dependable" callable (like a function).

            Don't call it directly, FastAPI will call it for you, just pass the object
            directly.
            """
        ),
    ] = None,
    *,

   * Does not close {@code appendable} if it is {@code Closeable}.
   *
   * @return the number of characters copied
   * @throws IOException if an I/O error occurs while reading from this source or writing to {@code
   *     appendable}
   */
  @CanIgnoreReturnValue
  public long copyTo(Appendable appendable) throws IOException {

Utiliser `BackgroundTasks` fonctionne aussi avec le système d'injection de dépendances. Vous pouvez déclarer un paramètre de type `BackgroundTasks` à différents niveaux : dans une *fonction de chemin*, dans une dépendance, dans une sous-dépendance...

**FastAPI** sait quoi faire dans chaque cas et comment réutiliser le même objet, afin que tous les paramètres de type `BackgroundTasks` soient fusionnés et que les tâches soient exécutées en arrière-plan :

* ⬆ Bump dawidd6/action-download-artifact from 2.9.0 to 2.21.1. PR [#5130](https://github.com/tiangolo/fastapi/pull/5130) by [@dependabot[bot]](https://github.com/apps/dependabot).
* ⬆ Bump actions/setup-python from 2 to 4. PR [#5129](https://github.com/tiangolo/fastapi/pull/5129) by [@dependabot[bot]](https://github.com/apps/dependabot).

import org.apache.maven.api.annotations.Nonnull;

/**
 * Message builder that supports configurable styling.
 *
 * @since 4.0.0
 * @see MessageBuilderFactory
 */
public interface MessageBuilder extends Appendable {

    /**
     * Append message content in trace style.
     * By default, bold magenta
     *
     * @param message the message to append
     * @return the current builder
     */
    @Nonnull

 * with maven-shared-utils, while Maven has migrated to JLine (into which Jansi has been merged
 * since JLine 3.25.0).
 */
@SuppressWarnings("unused")
public class Ansi implements Appendable {

    private static final char FIRST_ESC_CHAR = 27;
    private static final char SECOND_ESC_CHAR = '[';

    /**
     * <a href="https://en.wikipedia.org/wiki/ANSI_escape_code#Colors">ANSI 8 colors</a> for fluent API

people at Google, as well as:

Akhil Goel, akhilgoe, Alexander Pivovarov, Amir Samani, Andrew Goodbody, Andrey Portnoy, Anthony Platanios, bernardoArcari, Brett Taylor, buptzyb, Chao, Christian Clauss, Cocoa, Daniil Kutz, Darya Parygina, dependabot[bot], Dimitris Vardoulakis, Dragan Mladjenovic, Elfie Guo, eukub, Faijul Amin, flyingcat, Frédéric Bastien, ganyu.08, Georg Stefan Schmid, Grigory Reznikov, Harsha H S, Harshit Monish, Heiner, Ilia Sergachev, Jan, Jane Liu, Jaroslav Sevcik, Kaixi...