## An app with callbacks { #an-app-with-callbacks }

Let's see all this with an example.

Imagine you develop an app that allows creating invoices.

These invoices will have an `id`, `title` (optional), `customer`, and `total`.

## Custom CDN for JavaScript and CSS { #custom-cdn-for-javascript-and-css }

Let's say that you want to use a different <abbr title="Content Delivery Network">CDN</abbr>, for example you want to use `https://unpkg.com/`.

This could be useful if for example you live in a country that restricts some URLs.

### Disable the automatic docs { #disable-the-automatic-docs }

    "tax": 3.2,
    "tags": [
        "rock",
        "metal",
        "bar"
    ],
    "images": [
        {
            "url": "http://example.com/baz.jpg",
            "name": "The Foo live"
        },
        {
            "url": "http://example.com/dave.jpg",
            "name": "The Baz"
        }
    ]
}
```

/// info | 정보

`images` 키가 어떻게 이미지 객체 리스트를 갖는지 주목하세요.

///

Samples

        assertEquals("site:example.com", getAsQuery(Collections.singletonMap(k, new String[] { "example.com" })));
        assertEquals("site:test.org", getAsQuery(Collections.singletonMap(k, new String[] { " test.org " })));
        assertEquals("site:example.com site:test.org", getAsQuery(Collections.singletonMap(k, new String[] { "example.com", "test.org" })));
    }

    public void test_conditions_timestamp() {

   * until a nonzero result is found; imposes "dictionary order." If the end of one iterable is
   * reached, but not the other, the shorter iterable is considered to be less than the longer one.
   * For example, a lexicographical natural ordering over integers considers {@code [] < [1] < [1,
   * 1] < [1, 2] < [2]}.
   *
   * <p>Note that {@code Collections.reverseOrder(lexicographical(comparator))} is not equivalent to

* PostgreSQL
* MySQL
* SQLite
* Oracle
* Microsoft SQL Server, etc.

In this example, we'll use **SQLite**, because it uses a single file and Python has integrated support. So, you can copy this example and run it as is.

Later, for your production application, you might want to use a database server like **PostgreSQL**.

/// tip

     * <p>
     * Of the resources under the root directory, only those with paths starting with the base directory are traversed. The handler receives the relative path from the root directory. For example, if the root directory is <code>/aaa/bbb</code> and the base directory is <code>ccc/ddd</code>, and the resource <code>/aaa/bbb/ccc/ddd/eee.txt</code> exists, the handler receives the path <code>ccc/ddd/eee.txt</code>.
     * </p>
     *

Wenn wir also ein Pydantic-Objekt `user_in` erstellen, etwa so:

```Python
user_in = UserIn(username="john", password="secret", email="john.doe@example.com")
```

und wir rufen seine `.dict()`-Methode auf:

```Python
user_dict = user_in.dict()
```

```console
$ pip install "fastapi[standard]"

---> 100%
```

</div>

**Note**: Make sure you put `"fastapi[standard]"` in quotes to ensure it works in all terminals.

## Example { #example }

### Create it { #create-it }

Create a file `main.py` with:

```Python
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")