我正在阅读这个问题：
When does a pointer to a linked list change the actual list?
此处代码：

typclass Node:
    def __init__(self, val):
        self.val = val
        self.next = None

    def addNode(self, val):
        root = self
        while root.next is not None:
            root = root.next
        root.next = Node(val)

    def iterateLL(self):
        root = self
        print
        while root is not None:
            print(str(root.val) + " ", end="")
            root = root.next
        print()

if __name__ =="__main__":
    L = Node(1)
    L.addNode(2)
    L.addNode(3)
    L.addNode(4)

    # iterate through list and print:
    L.iterateLL()

    # changing value of pointer does not affect L
    P = L
    P = P.next
    L.iterateLL() # L is unchanged

    # changing "next" value of pointer does affect L
    P = L 
    P.next = P.next.next
    L.iterateLL() # now we've skipped node 2

    # changing data of pointer does affect L
    P = L
    P.val = 10
    L.iterateLL()e here

这里我不明白为什么当我们修改P或P上的任何动作时“L.iterateLL”的值被改变。如果它是“P.iterateLL”，那么我可以完全理解，因为P从L读取所有数据;然而，现在迭代L实际上并没有改变任何东西，从我理解P=L是P从L读取的单向引用，并没有改变L，那么为什么当我们修改P时L的数据会改变？或者这里P=L也是L=P？
先谢谢你