不必为你使用的所有标签都添加元数据。

///

### 使用你的标签 { #use-your-tags }

将 `tags` 参数和*路径操作*（以及 `APIRouter`）一起使用，将其分配给不同的标签：

{* ../../docs_src/metadata/tutorial004_py310.py hl[21,26] *}

/// info | 信息

阅读更多关于标签的信息[路径操作配置](path-operation-configuration.md#tags)。

///

### 查看文档 { #check-the-docs }

如果你现在查看文档，它们会显示所有附加的元数据：

<img src="/img/tutorial/metadata/image02.png">

### 标签顺序 { #order-of-tags }

每个标签元数据字典的顺序也定义了在文档用户界面显示的顺序。

   * #descendingMultiset()} will not reflect any changes you make to the behavior of methods such as
   * {@link #add(Object)} or {@link #pollFirstEntry}. This skeleton implementation correctly
   * delegates each of its operations to the appropriate methods of this {@code
   * ForwardingSortedMultiset}.
   *
   * <p>In many cases, you may wish to override {@link #descendingMultiset()} to return an instance

	err := b.iow.Close()

	// Wait for all data to be written before returning else it causes race conditions.
	// Race condition is because of io.PipeWriter implementation. i.e consider the following
	// sequent of operations:
	// 1) pipe.Write()
	// 2) pipe.Close()
	// Now pipe.Close() can return before the data is read on the other end of the pipe and written to the disk
	// Hence an immediate Read() on the file can return incorrect data.

   *
   * <p>If the mapped keys or values contain duplicates (according to {@link
   * Object#equals(Object)}), an {@code IllegalArgumentException} is thrown when the collection
   * operation is performed. (This differs from the {@code Collector} returned by {@link
   * Collectors#toMap(Function, Function)}, which throws an {@code IllegalStateException}.)
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)

    //                                               -------
    /**
     * Displays the details of a specific failure URL record.
     *
     * @param crudMode the CRUD operation mode (should be DETAILS)
     * @param id the ID of the failure URL record to display
     * @return HTML response for the failure URL details page
     */
    @Execute
    @Secured({ ROLE, ROLE + VIEW })

  }

  /**
   * Guaranteed to throw an exception and leave the map unmodified.
   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @CanIgnoreReturnValue
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  public <T extends B> @Nullable T putInstance(Class<T> type, T value) {

如果你宣告了回傳型別，FastAPI 會用它來進行資料的**驗證**、在 OpenAPI 中**文件化**、**過濾**，並使用 Pydantic 進行**序列化**。

/// tip

由於 Pydantic 會在 **Rust** 端進行序列化，宣告回傳型別可獲得比未宣告時高得多的**效能**。

///

### 非 async 的*路徑操作函式* { #non-async-path-operation-functions }

你也可以用一般的 `def` 函式（沒有 `async`），同樣用 `yield`。

FastAPI 會確保正確執行，不會阻塞事件迴圈。

因為這種情況下函式不是 async，正確的回傳型別會是 `Iterable[Item]`：

{* ../../docs_src/stream_json_lines/tutorial001_py310.py ln[27:30] hl[28] *}

{* ../../docs_src/server_sent_events/tutorial001_py310.py ln[1:25] hl[10:12,23] *}

/// tip | 提示

由于 Pydantic 会在**Rust** 端序列化它，相比未声明返回类型，你将获得更高的**性能**。

///

### 非 async 的*路径操作函数* { #non-async-path-operation-functions }

你也可以使用常规的 `def` 函数（没有 `async`），并以同样的方式使用 `yield`。

FastAPI 会确保其正确运行，从而不阻塞事件循环。

由于此时函数不是 async，正确的返回类型应为 `Iterable[Item]`：

// errSignatureMismatch means signature did not match.
var errSignatureMismatch = errors.New("Signature does not match")

// When upload object size is greater than 5G in a single PUT/POST operation.
var errDataTooLarge = errors.New("Object size larger than allowed limit")

// When upload object size is less than what was expected.
var errDataTooSmall = errors.New("Object size smaller than expected")

We create an async function `lifespan()` with `yield` like this:

{* ../../docs_src/events/tutorial003_py310.py hl[16,19] *}

Here we are simulating the expensive *startup* operation of loading the model by putting the (fake) model function in the dictionary with machine learning models before the `yield`. This code will be executed **before** the application **starts taking requests**, during the *startup*.