{* ../../docs_src/events/tutorial003.py hl[1,13] *}

A **context manager** in Python is something that you can use in a `with` statement, for example, `open()` can be used as a context manager:

```Python
with open("file.txt") as file:
    file.read()
```

In recent versions of Python, there's also an **async context manager**. You would use it with `async with`:

```Python

    }
  }

  /**
   * Returns true if this stream is open. A stream is open until either:
   *
   *  * A `SYN_RESET` frame abnormally terminates the stream.
   *  * Both input and output streams have transmitted all data and headers.
   *
   * Note that the input stream may continue to yield data even after a stream reports itself as
   * not open. This is because input data is buffered.
   */
  val isOpen: Boolean

    path = tmp_path / "test.txt"
    path.write_bytes(b"<file content>")
    path2 = tmp_path / "test2.txt"
    path2.write_bytes(b"<file content2>")

    client = TestClient(app)
    with path.open("rb") as file, path2.open("rb") as file2:
        response = client.post(
            "/files/",
            files=(
                ("files", ("test.txt", file)),
                ("files", ("test2.txt", file2)),
            ),

		t.SkipNow()
	}

	dbDSN := os.Getenv("GORM_DSN")
	if dbDSN == "" {
		dbDSN = "gorm:gorm@tcp(localhost:9910)/gorm?charset=utf8&parseTime=True&loc=Local"
	}
	nativeDB, err := sql.Open("mysql", dbDSN)
	if err != nil {
		t.Fatalf("Should open db success, but got %v", err)
	}

	conn := &wrapperConnPool{
		db: nativeDB,
		expect: []string{
			"SELECT VERSION()",

  /**
   * Invoked when an event source has been accepted by the remote peer and may begin transmitting
   * events.
   */
  open fun onOpen(
    eventSource: EventSource,
    response: Response,
  ) {
  }

  /**
   * TODO description.
   */
  open fun onEvent(
    eventSource: EventSource,
    id: String?,
    type: String?,
    data: String,
  ) {
  }

  /**

{!../../docs_src/events/tutorial002.py!}
```

此处，`shutdown` 事件处理器函数在 `log.txt` 中写入一行文本 `Application shutdown`。

/// info | "说明"

`open()` 函数中，`mode="a"` 指的是**追加**。因此这行文本会添加在文件已有内容之后，不会覆盖之前的内容。

///

/// tip | "提示"

注意，本例使用 Python `open()` 标准函数与文件交互。

这个函数执行 I/O（输入/输出）操作，需要等待内容写进磁盘。

但 `open()` 函数不支持使用 `async` 与 `await`。

因此，声明事件处理函数要使用 `def`，不能使用 `asnyc def`。

///

/// info | "说明"

{
    "description": "TensorFlow is an end-to-end open source platform for machine learning. It has a comprehensive, flexible ecosystem of tools, libraries, and community resources that lets researchers push the state-of-the-art in ML and developers easily build and deploy ML-powered applications.",
    "license": "Apache-2.0",
    "title": "TensorFlow",
    "upload_type": "software",
    "creators": [
        {
            "name": "TensorFlow Developers"
        }

        If you found a clear typo, please open a PR with a fix instead of opening an issue.

  - type: dropdown
    id: issue-type
    attributes:
      label: Issue type
      options:
        - Wrong or misleading information
        - Missing information
        - Styling or Accessibility
        - Typo (please open a PR instead)
    validations:
      required: true
  - type: textarea

  fun enqueueCancel() {
    cancel = true
  }

  override fun onOpen(
    eventSource: EventSource,
    response: Response,
  ) {
    get().log("[ES] onOpen", Platform.INFO, null)
    events.add(Open(eventSource, response))
    drainCancelQueue(eventSource)
  }

  override fun onEvent(
    eventSource: EventSource,
    id: String?,
    type: String?,
    data: String,
  ) {

// os.Lstat()
func Access(name string) (err error) {
	defer updateOSMetrics(osMetricAccess, name)(err)
	return access(name)
}

// Open captures time taken to call os.Open
func Open(name string) (f *os.File, err error) {
	defer updateOSMetrics(osMetricOpen, name)(err)
	return os.Open(name)
}

// OpenFileDirectIO captures time taken to call disk.OpenFileDirectIO