python - 如何在实例化之前更改 __init__ 参数

Question

我想实现这样一个简单的界面:

IsAllowed(perms=[IsAdmin(runtime_value) | HasPerm('*')])

由于一些变量在实例化时不可用，我不得不推迟对 perms=[IsAdmin() | 的评估HasPerm('*')] 到稍后的时间点(当 __call__ 被我正在使用的 FastAPI 网络框架调用 IsAllowed 时)。我最接近实现的是以下内容:

IsAllowed(perms = lambda runtime_value: [IsAdmin(runtime_value) | HasPerm('*')])


class IsAllowed(object):
    def __init__(self, perms=None):
        self.perms = perms
    def __call__(self, runtime_value):
        result = self.perms(runtime_value)
        return result

不，我的问题是，有什么方法可以使接口(interface)保持为 IsAllowed(perms=[IsAdmin(runtime_value) | HasPerm('*')]) 但是，以某种方式注入(inject) lambda 在实例化之前进入它？

我在考虑元类或利用 __init_subclass__ Hook ？有什么想法吗？

Answer 1

如果我正确理解你的问题，你想要这样的东西:

from typing import Any


class IsAllowed(object):
    def __init__(self, *perms):
        self.perms = perms


def __call__(self, args: list[Any]):
    return all(self.perms[i](args[i]) for i in range(len(args)))

checker = IsAllowed(IsAdmin, HasPerm)
checker(“somevalue”, “*”)

更新:

对于评论区提到的案例:

from typing import Any, Callable


class Operation:
    pass


class Or(Operation):
    def __init__(self, *funcs: Callable[[Any], bool]) -> None:
        self.funcs = funcs
        
    def __call__(self, val: Any) -> bool:
        return any(func(val) for func in self.funcs)
    
    def __or__(self, other: Operation) -> Operation:
        return Or(*self.funcs, other.func)


class Predicate:
    def __init__(self, func: Callable[[Any], bool]) -> None:
        self.func = func
        
    def __or__(self, other) -> Or:
        return Or(self.func, other.func)
    
    
def Is1(x: int) -> bool:
    return x == 1
    
    
def Is2(x: int) -> bool:
    return x == 2
    
    
def Is3(x: int) -> bool:
    return x == 3
    
    
def main() -> None:
    pred1 = Predicate(Is1)
    pred2 = Predicate(Is2) 
    pred3 = Predicate(Is3)
    
    fancy_pred = pred1 | pred2 | pred3
    
    for i in range(5):
        print(fancy_pred(i))


if __name__ == "__main__":
    main()