Python，无法从类对象获取信息

Question

So I have no idea what's causing this error. I don't know how to describe it without showing you, so here's the relevant part of my code:

class Node(object):
    def __init__(self, contents, children):
        self.contents = contents
        self.children = children


def makeNode(district, parent):
    new_contents = parent.contents
    new_contents.append(district)
    new = Node(new_contents, [])
    parent.children.append(new)
    return new


root = Node([], [])
data = [[1,1,'r'],[1,2,'d'],[1,2,'r'],[1,4,'d']]
makeNode(data, root)

Here's the problem: new.contents is changed as planned, but so is parent.contents. What happened?

Answer 1

As you've mentioned it in your comment, you've got to copy the contents pf 'parent.contents' into 'new_contents'. Otherwise, you're accessing the list by reference, which is obviously not what is intended.

So, your 'makeNode' function could start as follows:

def makeNode(district, parent):
    new_content = copy.deepcopy(parent.contents)
    ...

I hope, I could clear things up for later readers... ;)