动态查找和 "replace" 方法时发生冲突

Question

我有一个 class 由静态方法“列表”组成，A。我想用 class-装饰器 Meta 改变它的行为，它作用于特定的静态方法，在这个例子中 content，通过执行方法 m.

我最初的尝试 CASE=2 没有达到预期效果，所以我开始了案例研究。我引入了一个新的 class B，它与其他方法 info 的实现略有不同，但引发了一个有趣的错误，而新的 class C 只是没有方法，info.

案例 2：贪婪案例

d[i] = classmethod(lambda cls, *args: mcs.m( getattr(target_cls, i)(*args)) )运行不正常，可能嵌套的动态表达式太多了？

案例 1：本质上是案例 2，但表达式分为两行，有效

   o = getattr(target_cls, i)
   d[i] = classmethod(lambda cls, *args: mcs.m(o(*args)))

代码在这里

class Meta:

    def __new__(mcs, target_cls):
        if CASE == 1:
            print('case 1')
            d = {}
            for i in dir(target_cls):
                 if i == 'content':
                    o = getattr(target_cls, i)
                    d[i] = classmethod(lambda cls, *args: mcs.m(o(*args)))

        if CASE == 2:
            print('case 2')
            d = {}
            for i in dir(target_cls):
                 if i == 'content':
                    d[i] = classmethod(lambda cls, *args: mcs.m( getattr(target_cls, i)(*args)) )

        return type('AAA', (target_cls,), d)

    @classmethod
    def m(mcs, p):

        return '--> ', p


class A:

    @staticmethod
    def content(response):
        return 'static_method', response
    @staticmethod
    def info(response):
        return response


class B:

    @staticmethod
    def content(response):
        return 'static_method', response
    @staticmethod
    def info(response):
        response.sort()
        return response

class C:

    @staticmethod
    def content(response):
        return 'static_method', response

# call the "content" class-method of each class for all different cases
for cls in (A, B, C):
    print(cls.__name__)
    for case in range(1,3):
        CASE = case
        R = Meta(cls)
        try:
            print(R.content('ppp'))
        except Exception as e: print(e)
    
    print()

输出

A
case 1
('--> ', ('static_method', 'ppp'))
case 2
('--> ', 'ppp')        # no decoration

B
case 1
('--> ', ('static_method', 'ppp'))
case 2
'str' object has no attribute 'sort'  # <- complained about the other method

C              # <- this is ok BUT I removed the other method!
case 1
('--> ', ('static_method', 'ppp'))
case 2
('--> ', ('static_method', 'ppp'))  # <- here the decoration took place

问题是为什么情况 2 不工作，如果它是语言的限制那么是哪种？

附加问题：classB案例2的错误如何解释

Answer 1

我猜这个问题是由循环引起的，原因是每个语句 没有自己的范围 （在循环中）。通过将 i 作为 lambda 的关键参数传递，解决了问题。

class Meta:

    def __new__(mcs, target_cls):
        d = {}
        for i in dir(target_cls):
             if i == 'content':
                d[i] = classmethod(lambda cls, *args, m_name=i: mcs.m( getattr(target_cls, m_name)(*args)) )
    
        return type('AAA', (target_cls,), d)

    @classmethod
    def m(mcs, p):
        return '--> ', p

class A:

    @staticmethod
    def content(response):
        return 'static_method', response

    @staticmethod
    def info(response):
        return response

print(A.content)
print(Meta(A).content)
print(Meta(A).content('a'))
print(Meta(A).info)

输出

<function A.content at 0x7f04500740d0> # original static method
<bound method Meta.__new__.<locals>.<lambda> of <class '__main__.AAA'>> # class method
('--> ', ('static_method', 'a'))
<function A.info at 0x7f0450074040>

动态查找和 "replace" 方法时发生冲突

Conflicts when find and "replace" a method dynamically

metaprogramming

dynamic

python-3.x