It used custom types in its declarations instead of standard Python types, but it was still a huge step forward.

It also was one of the first frameworks to generate a custom schema declaring the whole API in JSON.

It was not based on a standard like OpenAPI and JSON Schema. So it wouldn't be straightforward to integrate it with other tools, like Swagger UI. But again, it was a very innovative idea.

                        largeSubProjectRegex.containsMatchIn(
                            it.name,
                        )
                    }.groupBy { it.getSubProjectSplitName().substringBefore('_') }
            functionalTestsWithSplit.forEach {
                assertAllSplitsArePresent(it.key, it.value)
                assertCorrectParameters(it.key, it.value)
            }
        }

        internally.

        The first time it is called it stores the result in the attribute
        `app.openapi_schema`, and next times it is called, it just returns that same
        result. To avoid the cost of generating the schema every time.

        If you need to modify the generated OpenAPI schema, you could modify it.

        Read more in the

* 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 might be useful, for example, to return custom headers or cookies.

## Return a `Response` { #return-a-response }

In fact, you can return any `Response` or any sub-class of it.

/// tip

`JSONResponse` itself is a sub-class of `Response`.

///

And when you return a `Response`, **FastAPI** will pass it directly.

                It could be any valid Pydantic *field* type. So, it doesn't have to
                be a Pydantic model, it could be other things, like a `list`, `dict`,
                etc.

                It will be used for:

                * Documentation: the generated OpenAPI (and the UI at `/docs`) will
                    show it as the response (JSON Schema).

The **server** program (for example **Uvicorn** via **FastAPI CLI**) is capable of interpreting these headers, and then passing that information to your application.

But for security, as the server doesn't know it is behind a trusted proxy, it won't interpret those headers.

/// note | Technical Details

* If you see the PR makes sense, or we discussed it and considered it should be accepted, you can add commits on top of the PR to tweak it, to add docs, tests, format, refactor, remove extra files, etc.
* Feel free to comment in the PR to ask for more information, to suggest changes, etc.
* Once you think the PR is ready, move it in the internal GitHub project for me to review it.

## FastAPI People PRs

        model.stages
            .filter { it.stageName <= StageName.READY_FOR_RELEASE }
            .flatMap { it.functionalTests }
            .filter { it.os == os && !it.testType.crossVersionTests }
            .forEach {
                buildType(FlakyTestQuarantine(model, stage, it))
            }

        model.stages
            .filter { it.stageName <= StageName.READY_FOR_RELEASE }

///

## Run it { #run-it }

After that, you just need to install `pytest`.

Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

<div class="termy">

```console
$ pip install pytest

---> 100%
```

</div>