<img src="/img/tutorial/dependencies/image02.png">

## Shortcut { #shortcut }

But you see that we are having some code repetition here, writing `CommonQueryParams` twice:

//// tab | Python 3.10+

```Python
commons: Annotated[CommonQueryParams, Depends(CommonQueryParams)]
```

////

//// tab | Python 3.10+ non-Annotated

Only keep parentheses if they exist in the source text. Do not add parentheses to terms that do not have them.

### Avoiding Repetition in Translation

When translating sentences, avoid unnecessary repetition of words or phrases that are implied in context.
- Merge repeated words naturally while keeping the meaning.
- Do **not** introduce extra words to replace repeated phrases unnecessarily.

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps { #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.

It has an integrated dependency injection system, inspired by Angular 2. It requires pre-registering the "injectables" (like all the other dependency injection systems I know), so, it adds to the verbosity and code repetition.

As the parameters are described with TypeScript types (similar to Python type hints), editor support is quite good.

* Partager des connexions à la base de données.
* Imposer la sécurité, l’authentification, des exigences de rôles, etc.
* Et bien d’autres choses ...

Tout cela, en minimisant la répétition de code.

## Premiers pas { #first-steps }

Voyons un exemple très simple. Il sera tellement simple qu’il n’est pas très utile, pour l’instant.

Comme les paramètres sont décrits avec des types TypeScript (similaires aux annotations de type de Python), la prise en charge
par l'éditeur est assez bonne.

Group       = "(" Expression ")" .
Option      = "[" Expression "]" .
Repetition  = "{" Expression "}" .
</pre>

<p>
Productions are expressions constructed from terms and the following
operators, in increasing precedence:
</p>
<pre class="grammar">
|   alternation
()  grouping
[]  option (0 or 1 times)
{}  repetition (0 to n times)
</pre>

<p>

 * </ul>
 *
 * @author Jim McMaster
 * @author Jige Yu
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EqualsTester {
  private static final int REPETITIONS = 3;

  private final List<List<Object>> equalityGroups = new ArrayList<>();
  private final RelationshipTester.ItemReporter itemReporter;

  /** Constructs an empty EqualsTester instance */
  public EqualsTester() {

 * to explicitly add another equivalence group.
 *
 * @author Gregory Kick
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EquivalenceTester<T> {
  private static final int REPETITIONS = 3;

  private final Equivalence<? super T> equivalence;
  private final RelationshipTester<T> delegate;
  private final List<T> items = new ArrayList<>();

 * to explicitly add another equivalence group.
 *
 * @author Gregory Kick
 * @since 10.0
 */
@GwtCompatible
@NullMarked
public final class EquivalenceTester<T> {
  private static final int REPETITIONS = 3;

  private final Equivalence<? super T> equivalence;
  private final RelationshipTester<T> delegate;
  private final List<T> items = new ArrayList<>();