## pytest.mark.anyio

If we want to call asynchronous functions in our tests, our test functions have to be asynchronous. AnyIO provides a neat plugin for this, that allows us to specify that some test functions are to be called asynchronously.

## HTTPX

Even if your **FastAPI** application uses normal `def` functions instead of `async def`, it is still an `async` application underneath.

**FastAPI** knows what to do in each case and how to reuse the same object, so that all the background tasks are merged together and are run in the background afterwards:


{* ../../docs_src/background_tasks/tutorial002_an_py310.py hl[13,15,22,25] *}

---

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.

The key features are:

* **Fast**: Very high performance, on par with **NodeJS** and **Go** (thanks to Starlette and Pydantic). [One of the fastest Python frameworks available](#performance).

///

### <a href="https://requests.readthedocs.io" class="external-link" target="_blank">Requests</a>

**FastAPI** ist eigentlich keine Alternative zu **Requests**. Der Umfang der beiden ist sehr unterschiedlich.

Es wäre tatsächlich üblich, Requests *innerhalb* einer FastAPI-Anwendung zu verwenden.

Dennoch erhielt FastAPI von Requests einiges an Inspiration.

        * Different `dependencies` can be applied to different routers.
    * These `dependencies` are run before the normal parameter dependencies. And normal dependencies are run too. They can be combined.
    * Dependencies declared in a router are executed first, then the ones defined in *path operation decorators*, and then the ones declared in normal parameters. They are all combined and executed.

rpp/72/ title: Starting With FastAPI and Examining Python's Import System - Episode 72 - author: Python Bytes FM author_link: https://pythonbytes.fm/ link: https://www.pythonpodcast.com/fastapi-web-application-framework-episode-259/ title: 'Do you dare to press "."? - Episode 247 - Dan #6: SQLModel - use the same models for SQL and FastAPI' - author: Podcast.`__init__` author_link: https://www.pythonpodcast.com/ link: https://www.pythonpodcast.com/fastapi-web-application-framework-episode-259/ title:...

<div style="text-align: left; direction: ltr;"> [...] I'm using <strong>FastAPI</strong> a ton these days. [...] I'm actually planning to use it for all of my team's <strong>ML services at Microsoft</strong>. Some of them are getting integrated into the core <strong>Windows</strong> product and some <strong>Office</strong> products."</div>

## Simple usage

If you look at it, *path operation functions* are declared to be used whenever a *path* and *operation* matches, and then **FastAPI** takes care of calling the function with the correct parameters, extracting the data from the request.

Actually, all (or most) of the web frameworks work in this same way.

You never call those functions directly. They are called by your framework (in this case, **FastAPI**).

# JSON Compatible Encoder

There are some cases where you might need to convert a data type (like a Pydantic model) to something compatible with JSON (like a `dict`, `list`, etc).

For example, if you need to store it in a database.

For that, **FastAPI** provides a `jsonable_encoder()` function.

## Using the `jsonable_encoder`

Let's imagine that you have a database `fake_db` that only receives JSON compatible data.

///

### 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.