**Example**

                ```python
                from fastapi import FastAPI

                app = FastAPI(
                    servers=[
                        {"url": "https://stag.example.com", "description": "Staging environment"},
                        {"url": "https://prod.example.com", "description": "Production environment"},
                    ]

                </mxCell>
                <mxCell id="29" value="&lt;font face=&quot;Roboto&quot; data-font-src=&quot;https://fonts.googleapis.com/css?family=Roboto&quot; style=&quot;font-size: 24px&quot;&gt;https://someapp.example.com&lt;/font&gt;" style="rounded=0;whiteSpace=wrap;html=1;fontStyle=1;strokeWidth=4;" parent="33" vertex="1">
                    <mxGeometry x="60" y="27" width="380" height="250" as="geometry"/>
                </mxCell>

        "Access-Control-Request-Headers": "X-Example",
    }
    response = client.options("/", headers=headers)
    assert response.status_code == 200, response.text
    assert response.text == "OK"
    assert (
        response.headers["access-control-allow-origin"]
        == "https://localhost.tiangolo.com"
    )
    assert response.headers["access-control-allow-headers"] == "X-Example"

    # Test standard response

  optional string type = 1;

  // object refers to a metric describing a single kubernetes object
  // (for example, hits-per-second on an Ingress object).
  // +optional
  optional ObjectMetricSource object = 2;

  // pods refers to a metric describing each pod in the current scale target
  // (for example, transactions-processed-per-second).  The values will be
  // averaged together before being compared to the target value.

  optional string type = 1;

  // object refers to a metric describing a single kubernetes object
  // (for example, hits-per-second on an Ingress object).
  // +optional
  optional ObjectMetricSource object = 2;

  // pods refers to a metric describing each pod in the current scale target
  // (for example, transactions-processed-per-second).  The values will be
  // averaged together before being compared to the target value.

This includes, for example:

* Email notifications sent after performing an action:
    * As connecting to an email server and sending an email tends to be "slow" (several seconds), you can return the response right away and send the email notification in the background.
* Processing data:

**FastAPI** provides a convenience tool to structure your application while keeping all the flexibility.

/// info

If you come from Flask, this would be the equivalent of Flask's Blueprints.

///

## An example file structure

Let's say you have a file structure like this:

```
.
├── app
│   ├── __init__.py
│   ├── main.py
│   ├── dependencies.py
│   └── routers
│   │   ├── __init__.py

 * {@code InetAddress.getAddress()}) they are 4 and 16 bytes in length, respectively, and represent
 * the address in network byte order.
 *
 * <p>Examples of IP addresses and their byte representations:
 *
 * <dl>
 *   <dt>The IPv4 loopback address, {@code "127.0.0.1"}.
 *   <dd>{@code 7f 00 00 01}
 *   <dt>The IPv6 loopback address, {@code "::1"}.

    open fun encode(codePoint: Int): String {
      throw UnsupportedOperationException()
    }
  }

  enum class Component {
    USER {
      override fun urlString(value: String): String = "http://$value@example.com/"

      override fun encodedValue(url: HttpUrl): String = url.encodedUsername

      override operator fun set(
        builder: HttpUrl.Builder,
        value: String,
      ) {

* You can check all the valid Pydantic data types here: <a href="https://docs.pydantic.dev/latest/usage/types/types/" class="external-link" target="_blank">Pydantic data types</a>.

## Example

Here's an example *path operation* with parameters using some of the above types.

//// tab | Python 3.10+

```Python hl_lines="1  3  12-16"
{!> ../../docs_src/extra_data_types/tutorial001_an_py310.py!}
```

////