interface Transformer {
        /**
         * Interpolate the value read from the xml document
         *
         * @param source    The source value
         * @param fieldName A description of the field being interpolated. The implementation may use this to
         *                  log stuff.
         * @return the interpolated value
         */
        String transform(String source, String fieldName);
    }

```{ .python .annotate hl_lines="2  10-12  14" }
{!../../docs_src/custom_response/tutorial008.py!}
```

1️⃣. 👉 🚂 🔢. ⚫️ "🚂 🔢" ↩️ ⚫️ 🔌 `yield` 📄 🔘.
2️⃣. ⚙️ `with` 🍫, 👥 ⚒ 💭 👈 📁-💖 🎚 📪 ⏮️ 🚂 🔢 🔨. , ⏮️ ⚫️ 🏁 📨 📨.
3️⃣. 👉 `yield from` 💬 🔢 🔁 🤭 👈 👜 🌟 `file_like`. & ⤴️, 🔠 🍕 🔁, 🌾 👈 🍕 👟 ⚪️➡️ 👉 🚂 🔢.

    , ⚫️ 🚂 🔢 👈 📨 "🏭" 👷 🕳 🙆 🔘.

* It can do something to that **response** or run any needed code.
* Then it returns the **response**.

/// note | "Technical Details"

If you have dependencies with `yield`, the exit code will run *after* the middleware.

If there were any background tasks (documented later), they will run *after* all the middleware.

///

## Create a middleware

* Ele pode fazer algo com essa **resposta** ou executar qualquer código necessário.
* Então ele retorna a **resposta**.

/// note | "Detalhes técnicos"

Se você tiver dependências com `yield`, o código de saída será executado *depois* do middleware.

Se houver alguma tarefa em segundo plano (documentada posteriormente), ela será executada *depois* de todo o middleware.

///

## Criar um middleware

			return err
		}
	case !f.Tag.IsEmpty():
		if err := e.EncodeElement(f.Tag, xml.StartElement{Name: xml.Name{Local: "Tag"}}); err != nil {
			return err
		}
	default:
		// Always print Prefix field when both And & Tag are empty
		if err := e.EncodeElement(f.Prefix, xml.StartElement{Name: xml.Name{Local: "Prefix"}}); err != nil {
			return err
		}
	}

	return e.EncodeToken(xml.EndElement{Name: start.Name})
}

  private final ImmutableList<Annotation> annotations;

  /**
   * An {@code AnnotatedType} instance, or {@code null} under Android VMs (possible only when using
   * the Android flavor of Guava). The field is declared with a type of {@code Object} to avoid
   * compatibility problems on Android VMs. The corresponding accessor method, however, can have the

    private static final char HANKAKU_KATAKANA_LAST_CHAR = HANKAKU_KATAKANA[HANKAKU_KATAKANA.length - 1];

    @Override
    public String normalize(final String s, final String field, final String... langs) {
        if (s.length() == 0) {
            return s;
        }
        if (s.length() == 1) {
            return hankakuKatakanaToZenkakuKatakana(s.charAt(0)) + "";
        }

                    if (v4src != null) {
                        Field field = InputSource.class.getDeclaredField("modelId");
                        field.setAccessible(true);
                        field.set(v4src, ModelProblemUtils.toId(model));
                    }
                } catch (Throwable t) {
                    // TODO: use a lazy source ?

    extends ForwardingMap<K, V> implements BiMap<K, V>, Serializable {

  @SuppressWarnings("nullness:initialization.field.uninitialized") // For J2KT (lateinit)
  private transient Map<K, V> delegate;

  @SuppressWarnings("nullness:initialization.field.uninitialized") // For J2KT (lateinit)
  @RetainedWith
  transient AbstractBiMap<V, K> inverse;

  /*
   * Per JDK: "the behavior of a map entry is undefined if the backing map has been modified after
   * the entry was returned by the iterator, except through the setValue operation on the map entry"
   * As such, this field must be cleared before every map mutation.
   *
   * Note about volatile: volatile doesn't make it safe to read from a mutable graph in one thread