Tree traversal - level order

tree_traversal_levelorder_iterative.py

from collections import deque

def levelorder_traversal_iterating(root):
    if not root:
        return []

    result = []
    # using queue
    queue = deque([root])
    while queue:
        # start a new level array
        result.append([])
        current_level_size = len(queue)
        # visit all items in the current level
        for i in range(current_level_size):
            current = queue.popleft()
            result[-1].append(current.val)
            if current.left:
                queue.append(current.left)
            if current.right:
                queue.append(current.right)

    return result