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}.

    (Exception: if the Program itself is interactive but does not
    normally print such an announcement, your work based on the Program
    is not required to print an announcement.)

These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the Program, and
can be reasonably considered independent and separate works in