奇怪的Python类行为

Question

I have created a simple class to manage tree of related objects:

class node(object):
    children = list([])

    def __init__(self, ID, *children):
        self.ID = ID
        for c in children:
            self.children.append(c)

    def add(self, *children ):
        for c in children:
            self.children.append(c)

    def __str__(self):
        return self.ID
    def __repr__(self):
        print self.ID, len(self.children)


root = node('1')
root.add( node('1.1', node('1.1.1')),
          node('1.2'))

for c in root.children:
    print c

I'm getting:

1.1.1
1.1
1.2

However I'm expecting just 1.1 and 1.2. What is my mistake?

thanks, Dmitry

Answer 1

self.children is referring to node.children , which is a class variable. There is only a single instance of your list that is shared across all instances of the class.

You need to make it an instance variable:

class Node(object):
    def __init__(self, id, *children):
        self.children = []

Also, __str__ and __repr__ should return strings that follow a certain format.

Answer 2

Place children = list([]) inside the __init__ method like this:

def __init__(self, ID, *children):
        self.ID = ID
        self.children = []
        for c in children:
            self.children.append(c)