* It takes each **request** that comes to your application.
* It can then do something to that **request** or run any needed code.
* Then it passes the **request** to be processed by the rest of the application (by some *path operation*).
* It then takes the **response** generated by the application (by some *path operation*).

You can import it directly from `fastapi`:

```python
from fastapi import Request
```

!!! tip
    When you want to define dependencies that should be compatible with both HTTP and WebSockets, you can define a parameter that takes an `HTTPConnection` instead of a `Request` or a `WebSocket`.

### What is "Mounting"

"Mounting" means adding a complete "independent" application in a specific path, that then takes care of handling all the sub-paths.

This is different from using an `APIRouter` as a mounted application is completely independent. The OpenAPI and docs from your main application won't include anything from the mounted application, etc.

Para esos casos, puedes usar el `jsonable_encoder` para convertir tus datos antes de pasarlos a la respuesta:

```Python hl_lines="4 6 20 21"
{!../../../docs_src/response_directly/tutorial001.py!}
```

!!! note "Detalles Técnicos"

### <a href="https://docs.pydantic.dev/" class="external-link" target="_blank">Pydantic</a>

Pydantic is a library to define data validation, serialization and documentation (using JSON Schema) based on Python type hints.

That makes it extremely intuitive.

It is comparable to Marshmallow. Although it's faster than Marshmallow in benchmarks. And as it is based on the same Python type hints, the editor support is great.

!!! check "**FastAPI** uses it to"

    ```Python hl_lines="25"
    {!> ../../../docs_src/security/tutorial002.py!}
    ```

## Get the user

`get_current_user` will use a (fake) utility function we created, that takes a token as a `str` and returns our Pydantic `User` model:

=== "Python 3.10+"

    ```Python hl_lines="19-22  26-27"
    {!> ../../../docs_src/security/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

## Hypercorn with Trio

FastAPI uses a **unique ID** for each *path operation*, it is used for the **operation ID** and also for the names of any needed custom models, for requests or responses.

You can customize that function. It takes an `APIRoute` and outputs a string.

For example, here it is using the first tag (you will probably have only one tag) and the *path operation* name (the function name).

!!! info "`@decorator` Info"
    That `@something` syntax in Python is called a "decorator".

    You put it on top of a function. Like a pretty decorative hat (I guess that's where the term came from).

    A "decorator" takes the function below and does something with it.

    In our case, this decorator tells **FastAPI** that the function below corresponds to the **path** `/` with an **operation** `get`.

```console
$ python -m pip install --upgrade pip

---> 100%
```

</div>

!!! tip
    Every time you install a new package with `pip` under that environment, activate the environment again.

    This makes sure that if you use a terminal program installed by that package, you use the one from your local environment and not any other that could be installed globally.

### Install requirements using pip