如何使用多重继承覆盖 `__new__`？

Question

我如何写一个默认的 __new__ 并做一些像这样的小改动：

class A:
    def __new__(cls, *args, **kwargs):
        retval = super().__new__(cls, *args, **kwargs)
        retval.tree_parent = None
        return retval

class B(A):
    def __init__(self, x):
        self.x = x

b = B(1)

由于多态链中的其他 classes，我收到不在此 class 控制中的参数传递错误：

TypeError: object() takes no parameters

Answer 1

默认的__new__可以像在traitlets模块中那样写：

def __new__(cls, *args, **kwargs):
    # This is needed because object.__new__ only accepts
    # the cls argument.
    new_meth = super(HasDescriptors, cls).__new__
    if new_meth is object.__new__:
        inst = new_meth(cls)
    else:
        inst = new_meth(cls, *args, **kwargs)
    # Do something with inst.
    return inst