property, getter, setter and del

class C(object):
    def __init__(self):
        self.__x = None
 
    @property
    def x(self):
        """I'm the 'x' property."""
        return self.__x
 
    @x.setter
    def x(self, value):
        self.__x = value
 
    @x.deleter
    def x(self):
        # del self.__x
        self.__x = None


if __name__=="__main__":
    c = C()
    print c.x
    c.x = 1
    print c.x
    del c.x
    # c.x = 1
    print c.x

>> None
>> 1
>> None

http://www.runoob.com/python/python-func-property.html
https://segmentfault.com/a/1190000007984750
https://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/001386820062641f3bcc60a4b164f8d91df476445697b9e000