Python 结构模式匹配 - 将 Object 传递给 case 语句

Question

这是我的代码

class BasePlayer:
    @staticmethod
    def walk(direction):
        print(f"I run into {direction}")

class Archer(BasePlayer):
    @staticmethod
    def shoot():
        print("shoot")

class Wizard(BasePlayer):
    @staticmethod
    def cast_spell():
        print("Spell casted")

def play(expr):
    match expr.split():
        case [("Archer" | "Wizard") as player, "walk", ("north" | "south" | "west" | "east") as direction]:
            Archer.walk(direction)
        case ["Archer", "shoot"]:
            Archer.shoot()
        case _:
            raise Exception("Command not working...")

play("Archer walk west")

到目前为止一切正常，但我希望在第一个 case 语句中，我希望这样做更通用，如下所示：

    case [(Archer | Wizard) as player, "walk", ("north" | "south" | "west" | "east") as direction]:
        player.walk(direction)

但是我不能在 case 语句中使用对象（模式不绑定 Archer）。如果我将它保留为字符串，player 将不是 class，而只是一个字符串。

有没有办法让它工作？

Answer 1

首先，expr 是 str 类型，expr.split() 生成 str 的 list。您需要将匹配语句的那部分更改为一个函数，该函数将生成您想要实际匹配的类型。

您将（或可能遇到）运行使用您的通用语句版本的问题的第二部分是，其中假定裸名是要进行赋值的变量到，因此需要一个解决方法（有关更多详细信息，请参阅该线程中的答案）。故障演示如下：：

>>> match some_expression:
...     case [(Archer | Wizard) as player, "walk", ("north" | "south" | "west" | "east") as direction]:
...         player.walk(direction)
... 
  File "<stdin>", line 2
SyntaxError: name capture 'Archer' makes remaining patterns unreachable

作为一个快速而肮脏的答案，我将做一些懒惰的事情并将子classes作为属性分配给一个空的class（以模拟导入一个包含这些可播放的模块类型，例如可玩单位的 unit 模块）。为实现您想要的 objective 应该做些什么的核心思想可能看起来像这样：

class unit():
    "pretend this is a module"

unit.Wizard = Wizard
unit.Archer = Archer

def parse(expr):
    # Parse the incoming expression to [BasePlayer, str, str, ...]
    # Defaults to BasePlayer for unknown unit type.
    r = expr.split()
    r[0] = getattr(unit, r[0], BasePlayer)
    return r

def play2(expr):          
    match(parse(expr)):  # use the above parse function to parse the expression
        case [(unit.Archer | unit.Wizard) as player, "walk", ("north" | "south" | "west" | "east") as direction]:
            player.walk(direction)
        case [unit.Archer as player, "shoot"]:
            player.shoot()
        case _:
            raise Exception("Command not working...")

正在试用 play2 函数：

>>> play2('Archer walk west')
I run into west
>>> play2('Wizard walk west')
I run into west
>>> play2('Archer shoot')
shoot
>>> play2('Wizard shoot')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 8, in play2
Exception: Command not working...

Python 结构模式匹配 - 将 Object 传递给 case 语句

Python Structural pattern matching - pass Object to case statement

python

python-3.10

structural-pattern-matching