human
I wrote the below code

    def getter(self):
        if self._items:
            return getattr(self[0], item_attr)
        else:
            return getattr(self, cont_attr)
    def setter(self, value):
        setattr(self, cont_attr, value)
        for item in self:
            setattr(item, item_attr, value)
    return property(fget=getter, fset=setter, doc=doc)

What's a good function header?
assistant
#Here's a good function header.

def optionalcascade(cont_attr, item_attr, doc=''):