Python中match/case无法使用列表元素作为case的解决方法咨询

我开发了一个依赖操作系统的程序，想用match/case语句结合函数把按键输入映射到对应值。针对不同操作系统，我把控制码存在不同元组里，尝试用以下代码（类外示例）在match/case里用元组元素作为case：

import os
import CONTROLS # 存储ASCII值的文件

# UP DOWN RIGHT LEFT
if os.name == "posix":
    CONTROL_CODES = range(65, 69)
else:
    CONTROL_CODES = (72, 80, 77, 75)

pressed = None
def _input_control_codes(char):
    global pressed
    match char:
        case CONTROL_CODES[0]: # UP
            pressed = CONTROLS.UP
            return
        case CONTROL_CODES[1]: # DOWN
            pressed = CONTROLS.DOWN
            return
        case CONTROL_CODES[2]: # RIGHT
            pressed = CONTROLS.RIGHT
            return
        case CONTROL_CODES[3]: # LEFT
            pressed = CONTROLS.LEFT
            return

_input_control_codes(65) # 示例
print(pressed)

运行后触发语法错误：

File "~/main.py", line 14
    case CONTROL_CODES[0]: # UP
                      ^
SyntaxError: invalid syntax

我想知道有没有不用if语句或手动写两个match/case语句的实现方式？

Python的match/case语句要求case分支的模式必须是字面量、常量、或结构化模式，不能直接使用变量索引（比如CONTROL_CODES[0]），这就是触发语法错误的原因。下面是几种符合需求的实现方式：

方法1：字典映射替代match/case #

这是最简洁的方式，直接构建控制码到目标值的映射字典，完全不需要match/case：

import os
import CONTROLS

# 构建对应系统的控制码映射字典
if os.name == "posix":
    control_map = {
        65: CONTROLS.UP,
        66: CONTROLS.DOWN,
        67: CONTROLS.RIGHT,
        68: CONTROLS.LEFT
    }
else:
    control_map = {
        72: CONTROLS.UP,
        80: CONTROLS.DOWN,
        77: CONTROLS.RIGHT,
        75: CONTROLS.LEFT
    }

pressed = None
def _input_control_codes(char):
    global pressed
    # 用字典get方法获取对应值，不存在则不修改pressed
    pressed = control_map.get(char, pressed)

_input_control_codes(65)
print(pressed)

方法2：枚举类封装控制码 #

如果想保留类似match/case的结构，可以先把控制码封装成枚举常量，这样就能在case分支里使用：

import os
import CONTROLS
from enum import Enum

# 根据系统定义枚举
if os.name == "posix":
    class ControlCode(Enum):
        UP = 65
        DOWN = 66
        RIGHT = 67
        LEFT = 68
else:
    class ControlCode(Enum):
        UP = 72
        DOWN = 80
        RIGHT = 77
        LEFT = 75

pressed = None
def _input_control_codes(char):
    global pressed
    match char:
        case ControlCode.UP.value:
            pressed = CONTROLS.UP
        case ControlCode.DOWN.value:
            pressed = CONTROLS.DOWN
        case ControlCode.RIGHT.value:
            pressed = CONTROLS.RIGHT
        case ControlCode.LEFT.value:
            pressed = CONTROLS.LEFT

_input_control_codes(65)
print(pressed)

方法3：提前解包变量+match/case #

提前把控制码的各个值解包到单独变量里，这样就能在case分支里直接使用这些变量（需Python 3.10+支持）：

import os
import CONTROLS

# UP DOWN RIGHT LEFT
if os.name == "posix":
    UP_CODE, DOWN_CODE, RIGHT_CODE, LEFT_CODE = range(65, 69)
else:
    UP_CODE, DOWN_CODE, RIGHT_CODE, LEFT_CODE = (72, 80, 77, 75)

pressed = None
def _input_control_codes(char):
    global pressed
    match char:
        case UP_CODE:
            pressed = CONTROLS.UP
        case DOWN_CODE:
            pressed = CONTROLS.DOWN
        case RIGHT_CODE:
            pressed = CONTROLS.RIGHT
        case LEFT_CODE:
            pressed = CONTROLS.LEFT

_input_control_codes(65)
print(pressed)

其中字典映射的方式性能最优、代码最简洁，推荐优先使用。

内容的提问来源于stack exchange，提问作者Alex L