Given the simplicity of Flask, it seemed like a good match for building APIs. The next thing to find was a "Django REST Framework" for Flask.

!!! check "Inspired **FastAPI** to"
    Be a micro-framework. Making it easy to mix and match the tools and parts needed.

    Have a simple and easy to use routing system.

    runs-on: ubuntu-latest
    steps:
      - name: Dump GitHub context
        env:
          GITHUB_CONTEXT: ${{ toJson(github) }}
        run: echo "$GITHUB_CONTEXT"
      - name: Decide whether the needed jobs succeeded or failed
        uses: re-actors/alls-green@release/v1
        with:

    Again, you can combine `dataclasses` with standard type annotations.

8. Notice that this *path operation function* uses regular `def` instead of `async def`.

    As always, in FastAPI you can combine `def` and `async def` as needed.

    If you need a refresher about when to use which, check out the section _"In a hurry?"_ in the docs about [`async` and `await`](../async.md#in-a-hurry){.internal-link target=_blank}.

```

</div>

That would work for most of the cases. 😎

You could use that command for example to start your **FastAPI** app in a container, in a server, etc.

## ASGI Servers

Let's go a little deeper into the details.

FastAPI uses a standard for building Python web frameworks and servers called <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr>. FastAPI is an ASGI web framework.

### Custom Generate Unique ID Function

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.

            """
            By default, after a dependency is called the first time in a request, if
            the dependency is declared again for the rest of the request (for example
            if the dependency is needed by several dependencies), the value will be
            re-used for the rest of the request.

            Set `use_cache` to `False` to disable this behavior and ensure the

    The `scope` `dict` and `receive` function are both part of the ASGI specification.

    And those two things, `scope` and `receive`, are what is needed to create a new `Request` instance.

    To learn more about the `Request` check <a href="https://www.starlette.io/requests/" class="external-link" target="_blank">Starlette's docs about Requests</a>.

[tool.pytest.ini_options]
addopts = [
  "--strict-config",
  "--strict-markers",
  "--ignore=docs_src",
]
xfail_strict = true
junit_family = "xunit2"
filterwarnings = [
    "error",
    # TODO: needed by asyncio in Python 3.9.7 https://bugs.python.org/issue45097, try to remove on 3.9.8
    'ignore:The loop argument is deprecated since Python 3\.8, and scheduled for removal in Python 3\.10:DeprecationWarning:asyncio',

* 🔥 Remove old internal GitHub Action watch-previews that is no longer needed. PR [#9730](https://github.com/tiangolo/fastapi/pull/9730) by [@tiangolo](https://github.com/tiangolo).

## Alternatives

I have been creating APIs with complex requirements for several years (Machine Learning, distributed systems, asynchronous jobs, NoSQL databases, etc), leading several teams of developers.

As part of that, I needed to investigate, test and use many alternatives.

The history of **FastAPI** is in great part the history of its predecessors.

As said in the section [Alternatives](alternatives.md){.internal-link target=_blank}: