Python3 tuple usage with custom datatypes

Question

This code intends to perform level order traversal for a tree. I am trying to store both level information and node element in the queue. But code gives error when I try to extract level element from the queue.

Can anyone explain why this code gives error when trying to access second element of tuple ? Is this intended usage of tuples incorrect ?

from collections import defaultdict
from queue import Queue

    class Node:
        def __init__(self,data):
            self.val = data
            self.left = None
            self.right = None

    def levelOrderTraversal(root):
        result = defaultdict(list)
        if not root:
            return result
        q = Queue()
        level = 0
        q.put((level, root))

        while not q.empty():
            e = q.get()
            level = e[0]
            #Above line throws error: TypeError: 'int' object is not subscriptable
            node = e[1]
            result[level].append(node.val)
            if node.left:
                q.put(level + 1, node.left)
            if node.right:
                q.put(level + 1, node.right)
        return result

    def test1():
        root = Node(1)
        root.left = Node(2)
        root.right = Node(3)        

        levelOrderTraversal(root)

    test1()

What's the error message you get?

simonz
– simonz

2018-05-27 15:45:23 +00:00
Commented May 27, 2018 at 15:45 — simonz
– simonz, Commented May 27, 2018 at 15:45

Md Johirul Islam · Accepted Answer · 2018-05-27 20:36:34Z

1

You are messing up while offering to the queue. Initially you are doing q.put((root,level)) and some other places you are doing q.put(level + 1,node.left),q.put(level + 1,node.right). See the following corrected code:

from collections import defaultdict
from queue import Queue

class Node:
    def __init__(self,data):
        self.val = data
        self.left = None
        self.right = None

def levelOrderTraversal(root):
    result = defaultdict(list)
    if not root:
        return result
    q = Queue()
    level = 0
    q.put((level, root))

    while not q.empty():
        e = q.get()
        level = e[0]
            #Throws error: TypeError: 'Node' object does not support indexing
        node = e[1]
        result[level].append(node.val)
        if node.left:
            q.put((level + 1,node.left))
        if node.right:
            q.put((level + 1,node.right))
    return result

def test1():
    root = Node(1)
    root.left = Node(2)
    root.right = Node(3)
    return levelOrderTraversal(root)

print(test1()) # prints defaultdict(<class 'list'>, {0: [1], 1: [2, 3]})

Working code in Ideone https://ideone.com/Xy0OR8

edited May 27, 2018 at 20:36

answered May 27, 2018 at 15:50

Md Johirul Islam

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3 Comments

lava Over a year ago

Thank you for pointing out that error. After the correction, I get a different error: level = e[0] TypeError: 'int' object is not subscriptable

Md Johirul Islam Over a year ago

I am not sure whether you are making other mistake. Please see the working code in Ideone i have added

lava Over a year ago

Thanks, there were some other syntax errors. I fixed them. Thanks for looking into it.

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