Return Inorder Traversal list

Question

I'm trying to return list from inorder traversal and below is my code. If my input is [1,2,3] and output should be [3,1,2], but I'm returning value none. Can you please suggest what is wrong in my code? Thanks.

def inorderTraversal(currentNode,output=None):

    if output==None:
        output=[]
    if currentNode.left:
        return inorderTraversal(currentNode.left,output)

    return output.append(currentNode.data)

    if currentNode.right:
        return inorderTraversal(currentNode.right,output)

Answer 1

The problem is this line:

return output.append(currentNode.data)

You are returning the value of append but that is None . append changes the list but it does not return the new value of the list. Do this instead.

output.append(currentNode.data)
return output