也許你要啟動新版本，或只是不想再跑它了。🤷

///

### Lifespan 函式 { #lifespan-function }

首先要注意的是，我們定義了一個帶有 `yield` 的 async 函式。這和帶有 `yield` 的依賴（Dependencies）非常相似。

{* ../../docs_src/events/tutorial003_py310.py hl[14:19] *}

函式在 `yield` 之前的部分，會在應用啟動前先執行。

`yield` 之後的部分，會在應用結束後再執行。

### 非同步內容管理器（Async Context Manager） { #async-context-manager }

你會看到這個函式被 `@asynccontextmanager` 裝飾。

它會把函式轉換成所謂的「**非同步內容管理器（async context manager）**」。

func (z *xlMetaDataDirDecoder) DecodeMsg(dc *msgp.Reader) (err error) {
	var field []byte
	_ = field
	var zb0001 uint32
	zb0001, err = dc.ReadMapHeader()
	if err != nil {
		err = msgp.WrapError(err)
		return
	}
	var zb0001Mask uint8 /* 1 bits */
	_ = zb0001Mask
	for zb0001 > 0 {
		zb0001--
		field, err = dc.ReadMapKeyPtr()
		if err != nil {
			err = msgp.WrapError(err)
			return
		}

          style: form
          explode: true
          schema:
            type: array
            items:
              type: string
            example: [name]
        - name: facet.field
          in: query
          description: Facet field name
          required: false
          style: form
          explode: true
          schema:
            type: array
            items:
              type: string

/// tip | 豆知識

async 関数内からブロッキングなコードを呼び出す必要がある場合、あるいはブロッキングな関数内から async 関数を呼び出す必要がある場合は、FastAPI の兄弟ライブラリである [Asyncer](https://asyncer.tiangolo.com) を利用できます。

///

### `yield from` { #yield-from }

ファイルライクオブジェクトのようなものをイテレートして各要素に対して `yield` している場合、`for` ループを省略して、`yield from` で各要素をそのまま送ることもできます。

これは FastAPI 固有ではなく単なる Python の機能ですが、知っておくと便利な小ワザです。 😎

        "Constructor" to "AddedClass()",
        "Class" to "AddedEnum",
        "Field" to "FOO"
    ) + reportedMembersFor("AddedEnum", isEnum = true) + listOf(
        "Method" to "AddedEnum.valueOf(java.lang.String)",
        "Method" to "AddedEnum.values()",
        "Class" to "AddedObject",
        "Field" to "INSTANCE",
        "Field" to "cathedral"

   * next} field is lazily initialized. The type of that field would be {@code @Nullable T}, and the
   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem

   * next} field is lazily initialized. The type of that field would be {@code @Nullable T}, and the
   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem

    }
  }

  @J2ktIncompatible
  @GwtIncompatible // reflection
  public void testConstants_charset() throws Exception {
    for (Field field : getConstantFields()) {
      Optional<Charset> charset = ((MediaType) field.get(null)).charset();
      if (field.getName().endsWith("_UTF_8")) {
        assertThat(charset).hasValue(UTF_8);
      } else {
        assertThat(charset).isAbsent();
      }
    }
  }

                    @Nullable public String foo() { return "bar"; }
                }
            """
        ) {
            assertHasErrors(
                "Field nonFinalField: Nullability breaking change.",
                "Field finalField: From non-nullable to nullable breaking change.",
                "Method com.example.Source.foo(): From non-null returning to null returning breaking change."
            )

        if (value instanceof final LocalDateTime ldt) {
            final ZonedDateTime zdt = ZonedDateTime.of(ldt, ZoneId.systemDefault());
            super.addFieldToSource(sourceMap, field, DateTimeFormatter.ISO_INSTANT.format(zdt));
        } else {
            super.addFieldToSource(sourceMap, field, value);
        }
    }

    @Override