If you pass a custom list of `servers` and there's a `root_path` (because your API lives behind a proxy), **FastAPI** will insert a "server" with this `root_path` at the beginning of the list.

For example:

```Python hl_lines="4-7"
{!../../../docs_src/behind_a_proxy/tutorial003.py!}
```

Will generate an OpenAPI schema like:

```JSON hl_lines="5-7"
{
    "openapi": "3.1.0",
    // More stuff here
    "servers": [

=== "Python 3.9+"

    ```Python hl_lines="1  11"
    {!> ../../../docs_src/settings/app03_an_py39/main.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="1  11"
    {!> ../../../docs_src/settings/app03_an/main.py!}
    ```

=== "Python 3.8+ non-Annotated"

    !!! tip
        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="1  10"

7. Set the current working directory to `/code`.

8. Copy the `requirements.txt` file to the `/code` directory.

    This file only lives in the previous Docker stage, that's why we use `--from-requirements-stage` to copy it.

9. Install the package dependencies in the generated `requirements.txt` file.

10. Copy the `app` directory to the `/code` directory.

You could also define it as a normal function instead of `async def`:

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial003.py!}
```

!!! note
    If you don't know the difference, check the [Async: *"In a hurry?"*](../async.md#in-a-hurry){.internal-link target=_blank}.

### Step 5: return the content

```Python hl_lines="8"
{!../../../docs_src/first_steps/tutorial001.py!}
```

   * provided that the function is capable of accepting null input. The transformed multimap might
   * contain null values, if the function sometimes gives a null result.
   *
   * <p>The returned multimap is not thread-safe or serializable, even if the underlying multimap
   * is. The {@code equals} and {@code hashCode} methods of the returned multimap are meaningless,

   * that the function is capable of accepting null input. The transformed map might contain null
   * values, if the function sometimes gives a null result.
   *
   * <p>The returned map is not thread-safe or serializable, even if the underlying map is.
   *
   * <p>The function is applied lazily, invoked when needed. This is necessary for the returned map

=== "Python 3.10+"

    ```Python hl_lines="68-69  82"
    {!> ../../../docs_src/websockets/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="68-69  82"
    {!> ../../../docs_src/websockets/tutorial002_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="69-70  83"
    {!> ../../../docs_src/websockets/tutorial002_an.py!}
    ```

---
hide:
  - navigation
---

# Features

## FastAPI features

**FastAPI** gives you the following:

### Based on open standards

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip

}

func parsEnvEntry(envEntry string) (envKV, error) {
	envEntry = strings.TrimSpace(envEntry)
	if envEntry == "" {
		// Skip all empty lines
		return envKV{
			Skip: true,
		}, nil
	}
	if strings.HasPrefix(envEntry, "#") {
		// Skip commented lines
		return envKV{
			Skip: true,
		}, nil
	}