对于在父类中存在的属性，如果要在其派生类中继续扩展属性

　　可以这样实现

class Valley:
    def __init__(self):
        self._name = None

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, val):
        try:
            assert val.startswith("g")
        except  AssertionError:
            self._name = "g" + val
        else:
            self._name = val


class SubValley(Valley):
    @Valley.name.setter
    def name(self, val):
        if len(val) >= 3:
            print(">>长度检查通过")
        else:
            raise Exception("{}长度应大于等于3".format(val))
        super(SubValley, SubValley).name.__set__(self, val)


if __name__ == '__main__':
    obj = SubValley()
    obj.name = 'lee'
    print(obj._name)

output:　

　　>>长度检查通过
　　glee