Chainnable object wrapper in Python

class Chain:
    def __init__(self, obj, root=None):
        self.__obj = obj
    def __getattr__(self, attr):
        val = getattr(self.__obj, attr)
        if callable(val):
            self.__callable = val
            return self
        return val
    def __call__(self, *args, **kw):
        val = self.__callable(*args, **kw)
        if val is None:
            return self
        return val