{* ../../docs_src/first_steps/tutorial001.py hl[7] *}

This is a Python function.

It will be called by **FastAPI** whenever it receives a request to the URL "`/`" using a `GET` operation.

In this case, it is an `async` function.

---

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

{* ../../docs_src/first_steps/tutorial003.py hl[7] *}

/// note

</details>

////

//// tab | Python 3.8+

```Python hl_lines="9"
{!> ../../docs_src/separate_openapi_schemas/tutorial001.py[ln:1-9]!}

# Code below omitted 👇
```

<details>
<summary>👀 Visualização completa do arquivo</summary>

```Python
{!> ../../docs_src/separate_openapi_schemas/tutorial001.py!}
```

</details>

////

### Modelo para Entrada

{* ../../docs_src/configure_swagger_ui/tutorial001.py hl[3] *}

...and then Swagger UI won't show the syntax highlighting anymore:

<img src="/img/tutorial/extending-openapi/image03.png">

## Change the Theme

The same way you could set the syntax highlighting theme with the key `"syntaxHighlight.theme"` (notice that it has a dot in the middle):

{* ../../docs_src/configure_swagger_ui/tutorial002.py hl[3] *}

{* ../../docs_src/python_types/tutorial003.py hl[1] *}

Because the editor knows the types of the variables, you don't only get completion, you also get error checks:

<img src="/img/python-types/image04.png">

Now you know that you have to fix it, convert `age` to a string with `str(age)`:

{* ../../docs_src/python_types/tutorial004.py hl[2] *}

## Declaring types

////

//// tab | Python 3.8+ non-Annotated

/// tip

Prefer to use the `Annotated` version if possible.

///

```Python hl_lines="8  49  56-57  60-61  70-76"
{!> ../../docs_src/security/tutorial004.py!}
```

////

/// note

If you check the new (fake) database `fake_users_db`, you will see how the hashed password looks like now: `"$2b$12$EixZaYVK1fsbw1ZfbX3OXePaWxn96p36WQoeG6Lruj3vjPGga31lW"`.

* 📝 Fix async test example not to trigger DeprecationWarning. PR [#12084](https://github.com/fastapi/fastapi/pull/12084) by [@marcinsulikowski](https://github.com/marcinsulikowski).
* 📝 Update `docs_src/path_params_numeric_validations/tutorial006.py`. PR [#11478](https://github.com/fastapi/fastapi/pull/11478) by [@MuhammadAshiqAmeer](https://github.com/MuhammadAshiqAmeer).