LeetCode 116 Populating Next Right Pointers in Each Node

# Definition for binary tree with next pointer.
# class TreeLinkNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#         self.next = None

class Solution(object):
    def connect(self, root):
        """
        :type root: TreeLinkNode
        :rtype: nothing
        """
        if root is None:
            return
        nodes = [root]
        while len(nodes) != 0:
            next_step = []
            last = None
            for node in nodes:
                if last is not None:
                    last.next = node
                if node.left is not None:
                    next_step.append(node.left)
                if node.right is not None:
                    next_step.append(node.right)
                last = node
            nodes = next_step