Python结构模式匹配 - 将对象传递给案例语句

Question

这是我到目前为止正常工作的代码

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")

，但是我想要在第一个case语句中，我想要这样做更通用：

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

但是我无法在案例语句中使用对象（模式没有模式绑定弓箭手）。如果我将其作为字符串留下，player将不是类，而只是字符串。

有没有办法做这项工作？

Answer 1

首先，expr是类型str和expr.split（）生成list> list of str。您需要将比赛语句的那部分更改为将产生您要实际匹配的类型的函数。

问题的第二部分（或可能已经存在）使用的通用语句版本为这个特定的问题，假定裸机是进行分配的变量，因此需要解决方法（有关更多详细信息，请参见该线程中的答案）。故障的演示如下：：

>>> 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，我将做懒惰的事情，并将子类作为属性分配给一个空类（以模拟导入包含这些可玩类型的模块，例如单元可播放单元的模块）。应采取什么措施实现所需目标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...")

尝试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...