Python pre order recursive binary tree traversal

Question

I have this code:

def recursionTravel(node, returnArr = []):
    if node:
        returnArr.append(node.data)
        if node.left: returnArr.append(recursionTravel(node.left, returnArr))
        if node.right: returnArr.append(recursionTravel(node.right, returnArr))
    return node.data

# Pre-order traversal
def pre_order(node):
    output = []
    if node:
        output.append(node.data)
        if node.left: output.append(recursionTravel(node.left))
        if node.right: output.append(recursionTravel(node.right))
    return output

Binary tree consists of Node: [5, 10, 2, 'leaf'] Output should be the same: [5, 10, 2, 'leaf']

Issue: Last element is missing in the return. Return value: [5, 10, 2]

Answer 1

Simply change the last line of recusiveTravel.

def RecusiveTravel(node, returnArr[]):
  if node:
    returnArr.append(node.data)
    if node.left: returnArr.append(recursionTravel(node.left, returnArr))
    if node.right: returnArr.append(recursionTravel(node.right, returnArr))
    return returnArr

No need for the preOrder function. Just call it from the recusive function. It should work.