小编Nik*_*las的帖子

我正在尝试用 Python 实现简化的术语重写系统 (TRS)/符号代数系统。为此，我真的希望能够在类实例实例化过程中的特定情况下拦截和修改操作数。我提出的解决方案是创建一个元类来修改类对象（类型为“type”）的典型调用行为。

class Preprocess(type):
    """
    Operation argument preprocessing Metaclass.
    Classes using this Metaclass must implement the 
        _preprocess_(*operands, **kwargs)
    classmethod.
    """

    def __call__(cls, *operands, **kwargs):
        pops, pargs = cls._preprocess_(*operands, **kwargs)
        return super(Preprocess, cls).__call__(*pops, **pargs)

一个示例情况是扩展嵌套操作 F(F(a,b),c)-->F(a,b,c)

class Flat(object):
    """
    Use for associative Operations to expand nested 
    expressions of same Head: F(F(x,y),z) => F(x,y,z)
    """
    __metaclass__ = Preprocess
    @classmethod
    def _preprocess_(cls, *operands, **kwargs):
        head = []
        for o in operands:
            if isinstance(o, cls):
                head += list(o.operands)
            else:
                head.append(o)
        return …