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:

=== "Python 3.10+"

    ```Python hl_lines="8-9"
    {!> ../../../docs_src/dependencies/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="8-11"

The idea is for the **FastAPI** community to be kind and welcoming. At the same time, don't accept bullying or disrespectful behavior towards others. We have to take care of each other.

---

Here's how to help others with questions (in discussions or issues):

### Understand the question

* Check if you can understand what is the **purpose** and use case of the person asking.

Wenn Sie Typer CLI installieren, können Sie die Vervollständigung installieren mit:

<div class="termy">

```console
$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.
```

</div>

### Dokumentationsstruktur

Die Dokumentation verwendet <a href="https://www.mkdocs.org/" class="external-link" target="_blank">MkDocs</a>.

# Query Parameters and String Validations

**FastAPI** allows you to declare additional information and validation for your parameters.

Let's take this application as example:

=== "Python 3.10+"

    ```Python hl_lines="7"
    {!> ../../../docs_src/query_params_str_validations/tutorial001_py310.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="9"
    {!> ../../../docs_src/query_params_str_validations/tutorial001.py!}
    ```

Instead of that, by being an "asynchronous" system, once finished, the task can wait in line a little bit (some microseconds) for the computer / program to finish whatever it went to do, and then come back to take the results and continue working with them.

Si vous installez Typer CLI, vous pouvez installer la complétion avec :

<div class="termy">

```console
$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.
```

</div>

### Apps et documentation en même temps

Si vous exécutez les exemples avec, par exemple :

<div class="termy">

```console

如果你已经安装 Typer CLI ，则可以使用以下命令安装自动补全功能：

<div class="termy">

```console
$ typer --install-completion

zsh completion installed in /home/user/.bashrc.
Completion will take effect once you restart the terminal.
```

</div>

### 文档架构

文档使用 <a href="https://www.mkdocs.org/" class="external-link" target="_blank">MkDocs</a> 生成。

在 `./scripts/docs.py` 中还有额外工具 / 脚本来处理翻译。

<a href="https://www.codacy.com/?utm_source=github&utm_medium=sponsors&utm_id=pioneers" target="_blank" title="Take code reviews from hours to minutes"><img src="https://fastapi.tiangolo.com/img/sponsors/codacy.png"></a>

<!-- /sponsors -->

```json
{"message": "Hello World"}
```

...this response will return:

```json
{
  "message": "Hello World"
}
```

Of course, you will probably find much better ways to take advantage of this than formatting JSON. 😉

## Default response class

When creating a **FastAPI** class instance or an `APIRouter` you can specify which response class to use by default.

                    for param in parameters
                    if param.get("required")
                }
                # Make sure required definitions of the same parameter take precedence
                # over non-required definitions
                all_parameters.update(required_parameters)
                operation["parameters"] = list(all_parameters.values())