* The **file** that can be **executed** by the operating system, for example: `python`, `python.exe` or `uvicorn`.
* A particular program while it is **running** on the operating system, using the CPU, and storing things on memory. This is also called a **process**.

### What is a Process

The word **process** is normally used in a more specific way, only referring to the thing that is running in the operating system (like in the last point above):

## Einfach und leistungsstark

Obwohl das hierarchische Dependency Injection System sehr einfach zu definieren und zu verwenden ist, ist es dennoch sehr mächtig.

Sie können Abhängigkeiten definieren, die selbst wiederum Abhängigkeiten definieren können.

That way, you can create a token with an expiration of, let's say, 1 week. And then when the user comes back the next day with the token, you know that user is still logged in to your system.

### Types and validation

These environment variables can only handle text strings, as they are external to Python and have to be compatible with other programs and the rest of the system (and even with different operating systems, as Linux, Windows, macOS).

That means that any value read in Python from an environment variable will be a `str`, and any conversion to a different type or validation has to be done in code.

    Then APIStar stopped to exist as a server and Starlette was created, and was a new better foundation for such a system. That was the final inspiration to build **FastAPI**.

    I consider **FastAPI** a "spiritual successor" to APIStar, while improving and increasing the features, typing system, and other parts, based on the learnings from all these previous tools.

## Used by **FastAPI**

# Classes as Dependencies

Before diving deeper into the **Dependency Injection** system, let's upgrade the previous example.

## A `dict` from the previous example

In the previous example, we were returning a `dict` from our dependency ("dependable"):

=== "Python 3.10+"

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

=== "Python 3.9+"

    ```Python hl_lines="11"

    In diesem Fall müssen Sie sich darüber keine Sorgen machen. 🤷

### Beispiele für Strategien für Vorab-Schritte

Es hängt **stark** davon ab, wie Sie **Ihr System bereitstellen**, und hängt wahrscheinlich mit der Art und Weise zusammen, wie Sie Programme starten, Neustarts durchführen, usw.

Hier sind einige mögliche Ideen:

* Selbst Abhängigkeiten können Abhängigkeiten haben, woraus eine Hierarchie oder ein **„Graph“ von Abhängigkeiten** entsteht.
* Alles **automatisch gehandhabt** durch das Framework.

    * All this would also work for deeply nested JSON objects.
* Convert from and to JSON automatically.
* Document everything with OpenAPI, that can be used by:
    * Interactive documentation systems.
    * Automatic client code generation systems, for many languages.
* Provide 2 interactive documentation web interfaces directly.

---

We just scratched the surface, but you already get the idea of how it all works.

* Wie man **Validierungseinschränkungen** wie `maximum_length` oder `regex` setzt.
* Ein sehr leistungsfähiges und einfach zu bedienendes System für **<abbr title="Dependency Injection – Einbringen von Abhängigkeiten: Auch bekannt als Komponenten, Ressourcen, Provider, Services, Injectables">Dependency Injection</abbr>**.