Make sure you create a [virtual environment](../virtual-environments.md){.internal-link target=_blank}, activate it, and then install it, for example:

```console
$ pip install python-multipart
```

///

## Import `Form`

Import `Form` from `fastapi`:

//// tab | Python 3.9+

```Python hl_lines="3"

Ele deve parecer exatamente como uma *operação de rota* normal do FastAPI:

* Ele provavelmente deveria ter uma declaração do corpo que deveria receber, por exemplo. `body: InvoiceEvent`.
* E também deveria ter uma declaração de um código de status de resposta, por exemplo. `response_model=InvoiceEventReceived`.

```Python hl_lines="16-18  21-22  28-32"
{!../../docs_src/openapi_callbacks/tutorial001.py!}
```

  // must start and end with an alphanumeric character (e.g. 'MyName',  or 'my.name',  or
  // '123-abc', regex used for validation is '([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9]') with an
  // optional DNS subdomain prefix and '/' (e.g. 'example.com/MyName')
  //
  // Required.
  optional string name = 1;

  // Expression represents the expression which will be evaluated by CEL. Must evaluate to bool.

If you need to enforce it, use `OAuth2PasswordRequestFormStrict` instead of `OAuth2PasswordRequestForm`.

///

* An optional `client_id` (we don't need it for our example).
* An optional `client_secret` (we don't need it for our example).

/// info

The `OAuth2PasswordRequestForm` is not a special class for **FastAPI** as is `OAuth2PasswordBearer`.

```

With a server that holds a certificate and a client that trusts it we have enough for an HTTPS
handshake. The best part of this example is that we don't need to make our test code insecure with a
a fake `HostnameVerifier` or `X509TrustManager`.

Certificate Authorities
-----------------------

The above example uses a self-signed certificate. This is convenient for testing but not

#### Non-calculated values

These are inappropriate uses of lazy types:

```groovy
class Example {
    Property<String> getSomeProperty()

    Example() {
        getSomeProperty().set("value")
        getSomeProperty().disallowChanges()
    }
}

class Example2 {
    Provider<String> getSomeProperty() {
        return project.provider(() -> "value")
    }
}
```

```

////

Caso um cliente tente enviar alguns dados **extras** nos **parâmetros de consulta**, eles receberão um retorno de **erro**.

Por exemplo, se o cliente tentar enviar um parâmetro de consulta `tool` com o valor `plumbus`, como:

```http
https://example.com/items/?limit=10&tool=plumbus
```

Eles receberão um retorno de **erro** informando-os que o parâmentro de consulta `tool` não é permitido:

```json

You will learn more about adding extra information later in the docs, when learning to declare examples.

/// warning

Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.
As these keys may not necessarily be part of the OpenAPI specification, some OpenAPI tools, for example [the OpenAPI validator](https://validator.swagger.io/), may not work with your generated schema.

///

### Docs for tests

Most of the tests actually run against the example source files in the documentation.

This helps to make sure that:

* The documentation is up-to-date.
* The documentation examples can be run as is.
* Most of the features are covered by the documentation, ensured by test coverage.

#### Apps and docs at the same time

If you run the examples with, e.g.:

<div class="termy">

```console

In all the docs there are examples compatible with each version of Python (when there's a difference).

For example "**Python 3.6+**" means it's compatible with Python 3.6 or above (including 3.7, 3.8, 3.9, 3.10, etc). And "**Python 3.9+**" means it's compatible with Python 3.9 or above (including 3.10, etc).