level order traversal of binary tree

1# To import queue datastructure
2import collections
3 
4# Code to implement a binary tree
5class TreeNode: 
6     def __init__(self, val):
7         self.val = val
8         self.left = None
9         self.right = None
10 
11# Function for level Order Traversal
12def levelOrderTraversal(root):
13    ans = []
14 
15    # Return Null if the tree is empty
16    if root is None:
17        return ans
18    
19    # Initialize queue 
20    queue = collections.deque()
21    queue.append(root)
22 
23    # Iterate over the queue until it's empty
24    while queue:
25        # Check the length of queue
26        currSize = len(queue)
27        currList = []
28 
29        while currSize > 0:
30            # Dequeue element
31            currNode = queue.popleft()
32            currList.append(currNode.val)
33            currSize -= 1
34 
35            # Check for left child
36            if currNode.left is not None:
37                queue.append(currNode.left)
38            # Check for right child
39            if currNode.right is not None:
40                queue.append(currNode.right)
41        
42        # Append the currList to answer after each iteration
43        ans.append(currList)
44 
45    # Return answer list
46    return ans
47 
48root = TreeNode(1)
49root.left = TreeNode(2)
50root.right = TreeNode(3)
51root.left.left = TreeNode(4)
52root.left.right = TreeNode(5)
53 
54# Check if the algorithm work
55print(levelOrderTraversal(root))
56