Das Erste, was auffällt, ist, dass wir eine asynchrone Funktion mit `yield` definieren. Das ist sehr ähnlich zu Abhängigkeiten mit `yield`.

{* ../../docs_src/events/tutorial003_py39.py hl[14:19] *}

Der erste Teil der Funktion, vor dem `yield`, wird ausgeführt **bevor** die Anwendung startet.

Und der Teil nach `yield` wird ausgeführt, **nachdem** die Anwendung beendet ist.

import jakarta.validation.constraints.Size;

/**
 * Form class for editing duplicate host configurations in the admin interface.
 * This form extends CreateForm to include fields necessary for updating existing duplicate host entries,
 * including tracking information for optimistic locking and audit trails.

        int unknownClass = 1234;
        String expected = "unknown error class: 1234";
        assertEquals(expected, NbtException.getErrorString(unknownClass, 0));
    }

    @Test
    @DisplayName("Constructor sets fields and message correctly")
    void testConstructor() {
        NbtException e = new NbtException(NbtException.ERR_SSN_SRVC, NbtException.CONNECTION_REFUSED);
        assertEquals(NbtException.ERR_SSN_SRVC, e.errorClass);

      <releases>
        <!-- That's the boolean POM field we would like to interpolate -->
        <enabled>${releasesEnabled}</enabled>
      </releases>
    </repository>
  </repositories>

  <build>
    <resources>
      <resource>
        <directory>src/main/resources</directory>
        <!-- That's the boolean POM field we would like to interpolate -->
        <filtering>${filter.resources}</filtering>

Вы можете проверить это в интерфейсе документации по адресу `/docs`:

<div class="screenshot">
<img src="/img/tutorial/request-form-models/image01.png">
</div>

## Запрет дополнительных полей формы { #forbid-extra-form-fields }

В некоторых случаях (не особо часто встречающихся) вам может понадобиться **ограничить** поля формы только теми, которые объявлены в Pydantic-модели. И **запретить** любые **дополнительные** поля.

/// note | Заметка

### API Change

}

func ExampleFields() {
	fmt.Printf("Fields are: %q", bytes.Fields([]byte("  foo bar  baz   ")))
	// Output: Fields are: ["foo" "bar" "baz"]
}

func ExampleFieldsFunc() {
	f := func(c rune) bool {
		return !unicode.IsLetter(c) && !unicode.IsNumber(c)
	}
	fmt.Printf("Fields are: %q", bytes.FieldsFunc([]byte("  foo1;bar2,baz3..."), f))
	// Output: Fields are: ["foo1" "bar2" "baz3"]
}

	Metrics bool   `msg:"m"`
	NoOp    bool   `msg:"np"`
}

// DiskInfo is an extended type which returns current
// disk usage per path.
// The above means that any added/deleted fields are incompatible.
//
// The above means that any added/deleted fields are incompatible.
//
//msgp:tuple DiskInfo
type DiskInfo struct {
	Total      uint64
	Free       uint64
	Used       uint64
	UsedInodes uint64
	FreeInodes uint64

from typing import Annotated, Optional

import pytest
from fastapi import Body, FastAPI
from fastapi.testclient import TestClient
from pydantic import BaseModel, Field

from .utils import get_body_model_name

app = FastAPI()

# =====================================================================================
# Without aliases


@app.post("/optional-str", operation_id="optional_str")

Lo primero que hay que notar es que estamos definiendo una función asíncrona con `yield`. Esto es muy similar a las Dependencias con `yield`.

{* ../../docs_src/events/tutorial003_py39.py hl[14:19] *}

La primera parte de la función, antes del `yield`, será ejecutada **antes** de que la aplicación comience.

Y la parte después del `yield` será ejecutada **después** de que la aplicación haya terminado.