within such NOTICE file, excluding those notices that do not
          pertain to any part of the Derivative Works, in at least one
          of the following places: within a NOTICE text file distributed
          as part of the Derivative Works; within the Source form or
          documentation, if provided along with the Derivative Works; or,

          within such NOTICE file, excluding those notices that do not
          pertain to any part of the Derivative Works, in at least one
          of the following places: within a NOTICE text file distributed
          as part of the Derivative Works; within the Source form or
          documentation, if provided along with the Derivative Works; or,

          within such NOTICE file, excluding those notices that do not
          pertain to any part of the Derivative Works, in at least one
          of the following places: within a NOTICE text file distributed
          as part of the Derivative Works; within the Source form or
          documentation, if provided along with the Derivative Works; or,

### We Make Mistakes

We, as humans, make **mistakes**, all the time. Software almost *always* has **bugs** hidden in different places. 🐛

And we as developers keep improving the code as we find those bugs and as we implement new features (possibly adding new bugs too 😅).

### Small Errors Automatically Handled

We are going to include this `APIRouter` in the main `FastAPI` app, but first, let's check the dependencies and another `APIRouter`.

## Dependencies

We see that we are going to need some dependencies used in several places of the application.

So we put them in their own `dependencies` module (`app/dependencies.py`).

We will now use a simple dependency to read a custom `X-Token` header:

=== "Python 3.9+"

### Resumen

En resumen, declaras los tipos de parámetros, body, etc. **una vez** como parámetros de la función.

Lo haces con tipos modernos estándar de Python.

No tienes que aprender una sintaxis nueva, los métodos o clases de una library específica, etc.

Solo **Python 3.8+** estándar.

Por ejemplo, para un `int`:

```Python
item_id: int
```

o para un modelo más complejo de `Item`:

```Python

    * `alias_priority`
    * `validation_alias`
    * `serialization_alias`
    * `discriminator`
    * `strict`
    * `multiple_of`
    * `allow_inf_nan`
    * `max_digits`
    * `decimal_places`
    * `json_schema_extra`

...you can read about them in the Pydantic docs.

* The parameter `regex` has been deprecated and replaced by `pattern`.

    `Cookie` es una clase "hermana" de `Path` y `Query`. También hereda de la misma clase común `Param`.

    Pero recuerda que cuando importas `Query`, `Path`, `Cookie`  y otros de `fastapi`, en realidad son funciones que devuelven clases especiales.

!!! info
    Para declarar cookies, necesitas usar `Cookie`, porque de lo contrario los parámetros serían interpretados como parámetros de query.

## Resumen

It can't handle nested models very well. So, if the JSON body in the request is a JSON object that has inner fields that in turn are nested JSON objects, it cannot be properly documented and validated.

**Spoiler alert**: the tutorial - user guide includes:

* Declaration of **parameters** from other different places as: **headers**, **cookies**, **form fields** and **files**.
* How to set **validation constraints** as `maximum_length` or `regex`.