## Do not Separate Schemas { #do-not-separate-schemas }

Now, there are some cases where you might want to have the **same schema for input and output**.

Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

  protected CountDownLatch latch;
  protected ListenableFuture<Boolean> future;

  @Override
  protected void setUp() throws Exception {

    // Create a latch and a future that waits on the latch.
    latch = new CountDownLatch(1);
    future = createListenableFuture(Boolean.TRUE, null, latch);
  }

  @Override
  protected void tearDown() throws Exception {

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

```Python hl_lines="3" title="app/internal/admin.py"
{!../../docs_src/bigger_applications/app/internal/admin.py!}
```

But we still want to set a custom `prefix` when including the `APIRouter` so that all its *path operations* start with `/admin`, we want to secure it with the `dependencies` we already have for this project, and we want to include `tags` and `responses`.

		version string
		format  string
		want    bool
	}{
		{1, "123", "fs", false},
		{2, "123", xlMetaFormat, false},
		{3, xlMetaVersion100, "test", false},
		{4, xlMetaVersion101, "hello", false},
		{5, xlMetaVersion100, xlMetaFormat, true},
		{6, xlMetaVersion101, xlMetaFormat, true},
	}
	for _, tt := range tests {
		if got := isXLMetaFormatValid(tt.version, tt.format); got != tt.want {

<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

This is probably not as important or necessary if you use `Annotated`.

///

Let's say that you want to declare the query parameter `q` as a required `str`.

And you don't need to declare anything else for that parameter, so you don't really need to use `Query`.

But you still need to use `Path` for the `item_id` path parameter. And you don't want to use `Annotated` for some reason.

func bitrotVerify(r io.Reader, wantSize, partSize int64, algo BitrotAlgorithm, want []byte, shardSize int64) error {
	if algo != HighwayHash256S {
		h := algo.New()
		if n, err := io.Copy(h, r); err != nil || n != wantSize {
			// Premature failure in reading the object, file is corrupt.
			return errFileCorrupt
		}
		if !bytes.Equal(h.Sum(nil), want) {
			return errFileCorrupt
		}
		return nil
	}

* <a href="https://jinja.palletsprojects.com" target="_blank"><code>jinja2</code></a> - Required if you want to use the default template configuration.

  protected CountDownLatch latch;
  protected ListenableFuture<Boolean> future;

  @Override
  protected void setUp() throws Exception {

    // Create a latch and a future that waits on the latch.
    latch = new CountDownLatch(1);
    future = createListenableFuture(Boolean.TRUE, null, latch);
  }

  @Override
  protected void tearDown() throws Exception {