iter_traverse

from collections import deque
from operator import attrgetter


class Node:
    def __init__(self, name):
        self.children = []
        self.name = name

    def addChild(self, child):
        self.children.append(child)

    def __repr__(self):
        return "Node('{}')".format(self.name)


def iter_traverse(node, attribute="children"):
    seen = set()
    stack = deque([node])
    result = []
    getter = attrgetter(attribute)
    while stack:
        node = stack.popleft()
        node_id = id(node)
        if node_id not in seen:
            seen.add(node_id)
            result.append(node)
        children = getter(result[-1])
        for child in children:
            stack.append(child)
    return result


node1 = Node("one")
node2 = Node("two")
node3 = Node("three")
[node3.addChild(Node("N{}".format(x))) for x in range(5)]
node4 = Node("four")
node1.addChild(node2)
node2.addChild(node3)
node3.addChild(node4)
node3.addChild(node1) # CYCLE!

print(iter_traverse(node1))
# [Node('one'), Node('two'), Node('three'), Node('N0'), Node('N1'), Node('N2'), Node('N3'), Node('N4'), Node('four')]