The [bytes] package adds several functions that work with iterators:
- [Lines] returns an iterator over the
  newline-terminated lines in the byte slice s.
- [SplitSeq] returns an iterator over
  all substrings of s separated by sep.
- [SplitAfterSeq] returns an iterator
  over substrings of s split after each instance of sep.
- [FieldsSeq] returns an iterator over
  substrings of s split around runs of whitespace characters,
  as defined by unicode.IsSpace.

# Middleware

There are several middlewares available provided by Starlette directly.

Read more about them in the [FastAPI docs for Middleware](https://fastapi.tiangolo.com/advanced/middleware/).

::: fastapi.middleware.cors.CORSMiddleware

It can be imported from `fastapi`:

```python
from fastapi.middleware.cors import CORSMiddleware
```

::: fastapi.middleware.gzip.GZipMiddleware

It can be imported from `fastapi`:

///

### Flask REST frameworks

There are several Flask REST frameworks, but after investing the time and work into investigating them, I found that many are discontinued or abandoned, with several standing issues that made them unfit.

### <a href="https://marshmallow.readthedocs.io/en/stable/" class="external-link" target="_blank">Marshmallow</a>

  /**
   * Schedules the request to be executed at some point in the future.
   *
   * The [dispatcher][OkHttpClient.dispatcher] defines when the request will run: usually
   * immediately unless there are several other requests currently being executed.
   *
   * This client will later call back `responseCallback` with either an HTTP response or a failure
   * exception.
   *

│   ├── dependencies.py
│   └── routers
│   │   ├── __init__.py
│   │   ├── items.py
│   │   └── users.py
│   └── internal
│       ├── __init__.py
│       └── admin.py
```

/// tip

There are several `__init__.py` files: one in each directory or subdirectory.

This is what allows importing code from one file into another.

For example, in `app/main.py` you could have a line like:

```
from app.routers import items

        api("org.ow2.asm:asm:$asmVersion")
        api("org.ow2.asm:asm-commons:$asmVersion")
        api("org.ow2.asm:asm-tree:$asmVersion")
        api("xerces:xercesImpl:2.12.2") {
            because("Maven Central and JCenter disagree on version 2.9.1 metadata")
        }
        api("net.bytebuddy:byte-buddy") { version { strictly("1.10.21") } }
        api("org.objenesis:objenesis") { version { strictly("3.1") } }
    }

We create an `HTTPException` that we can reuse (`raise`) later at several points.

In this exception, we include the scopes required (if any) as a string separated by spaces (using `scope_str`). We put that string containing the scopes in the `WWW-Authenticate` header (this is part of the spec).

1020901 E MN09 Morningside Heights 3802 41 220 1 Manhattan 022000 1022000 E MN11 Central Harlem South 3803 3389527 2 2014-03-13 17:32:49 2014-03-13 17:39:48 N 1 -73.952896118164062 40.810546875 -73.954177856445313 40.800579071044922 1 0.73 5.5 1 0.5 0 0 7 2 1 166 41 green 0.00 0.0 0.0 32 18 14.09 1312 209.01 1 Manhattan 020901 1020901 E MN09 Morningside Heights 3802 1836 216 1 Manhattan 021600 1021600 E MN11 Central Harlem South 3803 3389528 2 2014-03-17 12:05:03 2014-03-17 12:09:49 N 1 -73.953781127929688...

```

////

//// tab | Python 3.8+

```Python hl_lines="81-83"
{!> ../../docs_src/websockets/tutorial003.py!}
```

////

To try it out:

* Open the app with several browser tabs.
* Write messages from them.
* Then close one of the tabs.

That will raise the `WebSocketDisconnect` exception, and all the other clients will receive a message like:

```

import java.io.Serializable;
import java.util.Arrays;
import java.util.Comparator;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/** An ordering that tries several comparators in order. */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class CompoundOrdering<T extends @Nullable Object> extends Ordering<T>
    implements Serializable {