实例的属性可变吗？

Question

我已经在python中定义了一个类对象。但是，instance属性之一是引用另一个类的实例。我的问题是，实例的属性可变吗？类对象是不可变的？

## This is the class object:
class node(object):
    def __init__(self,data=None):
        self.data = data
        self.next =None

## I have the following code
current = node(1)
current.next = node(2)

previous = node(11)
next_1 = current.next
current.next = previous

## if current.next is mutable, once I reset current.next to be equal to previous, the value of next_1 will be changed