Sie könnten zum Beispiel eine Datei `main.py` haben mit:

```Python hl_lines="3"
import os

name = os.getenv("MY_NAME", "World")
print(f"Hello {name} from Python")
```

/// tip | "Tipp"

	TCPListener = wellknown.TCPProxy

	IPMatcher = "type.googleapis.com/xds.type.matcher.v3.IPMatcher"
)

// ListenerFilter is used to pass filter information into listener based config writer print functions
type ListenerFilter struct {
	Address string
	Port    uint32
	Type    string
	Verbose bool
}

// Verify returns true if the passed listener matches the filter fields

```Python hl_lines="2-5  15  21"
{!../../docs_src/handling_errors/tutorial006.py!}
```

		if err != nil {
			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
			return
		}
		copy(objectEncryptionKey[:], key)

		var nonce [12]byte
		tmp := sha256.Sum256([]byte(fmt.Sprint(uploadID, partID)))
		copy(nonce[:], tmp[:12])

		partEncryptionKey := objectEncryptionKey.DerivePartKey(uint32(partID))
		encReader, err := sio.EncryptReader(reader, sio.Config{
			Key:          partEncryptionKey[:],

			}
			return written, nil
		}
	}
}

// SafeClose safely closes any channel of any type
func SafeClose[T any](c chan<- T) {
	if c != nil {
		close(c)
		return
	}
	// Print stack to check who is sending `c` as `nil`
	// without crashing the server.
	debug.PrintStack()

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

在底层，`open("./somefile.txt")`创建了一个被称为"上下文管理器"的对象。

当 `with` 代码块结束时，它会确保关闭文件，即使发生了异常也是如此。

当你使用 `yield` 创建一个依赖项时，**FastAPI** 会在内部将其转换为上下文管理器，并与其他相关工具结合使用。

### 在使用 `yield` 的依赖项中使用上下文管理器

```Python hl_lines="2-5  15  21"
{!../../docs_src/handling_errors/tutorial006.py!}
```

errors.invalid_header_for_request_file=Invalid header: {0}
errors.could_not_delete_logged_in_user=Could not delete logged in user.
errors.unauthorized_request=Unauthorized request.
errors.failed_to_print_thread_dump=Failed to print thread dump.
errors.file_is_not_supported={0} is not supported.
errors.plugin_file_is_not_found={0} is not found.
errors.failed_to_install_plugin=Failed to install {0}.

errors.invalid_header_for_request_file=Invalid header: {0}
errors.could_not_delete_logged_in_user=Could not delete logged in user.
errors.unauthorized_request=Unauthorized request.
errors.failed_to_print_thread_dump=Failed to print thread dump.
errors.file_is_not_supported={0} is not supported.
errors.plugin_file_is_not_found={0} is not found.
errors.failed_to_install_plugin=Failed to install {0}.

				"application/vnd.pwg-multiplexed",
				"application/vnd.pwg-xhtml-print+xml",
				"application/vnd.qualcomm.brew-app-res",
				"application/vnd.quark.quarkxpress",
				"application/vnd.rapid",
				"application/vnd.recordare.musicxml",
				"application/vnd.recordare.musicxml+xml",
				"application/vnd.renlearn.rlprint",
				"application/vnd.rim.cod",
				"application/vnd.rn-realmedia",