#### Binary Tree Traversal

```# flake8: noqa

"""
This is pure Python implementation of tree traversal algorithms
"""
from __future__ import annotations

import queue

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

def build_tree():
print("\n********Press N to stop entering at any point of time********\n")
check = input("Enter the value of the root node: ").strip().lower() or "n"
if check == "n":
return None
q: queue.Queue = queue.Queue()
tree_node = TreeNode(int(check))
q.put(tree_node)
while not q.empty():
node_found = q.get()
msg = "Enter the left node of %s: " % node_found.data
check = input(msg).strip().lower() or "n"
if check == "n":
return tree_node
left_node = TreeNode(int(check))
node_found.left = left_node
q.put(left_node)
msg = "Enter the right node of %s: " % node_found.data
check = input(msg).strip().lower() or "n"
if check == "n":
return tree_node
right_node = TreeNode(int(check))
node_found.right = right_node
q.put(right_node)

def pre_order(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> pre_order(root)
1,2,4,5,3,6,7,
"""
if not isinstance(node, TreeNode) or not node:
return
print(node.data, end=",")
pre_order(node.left)
pre_order(node.right)

def in_order(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> in_order(root)
4,2,5,1,6,3,7,
"""
if not isinstance(node, TreeNode) or not node:
return
in_order(node.left)
print(node.data, end=",")
in_order(node.right)

def post_order(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> post_order(root)
4,5,2,6,7,3,1,
"""
if not isinstance(node, TreeNode) or not node:
return
post_order(node.left)
post_order(node.right)
print(node.data, end=",")

def level_order(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> level_order(root)
1,2,3,4,5,6,7,
"""
if not isinstance(node, TreeNode) or not node:
return
q: queue.Queue = queue.Queue()
q.put(node)
while not q.empty():
node_dequeued = q.get()
print(node_dequeued.data, end=",")
if node_dequeued.left:
q.put(node_dequeued.left)
if node_dequeued.right:
q.put(node_dequeued.right)

def level_order_actual(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> level_order_actual(root)
1,
2,3,
4,5,6,7,
"""
if not isinstance(node, TreeNode) or not node:
return
q: queue.Queue = queue.Queue()
q.put(node)
while not q.empty():
list = []
while not q.empty():
node_dequeued = q.get()
print(node_dequeued.data, end=",")
if node_dequeued.left:
list.append(node_dequeued.left)
if node_dequeued.right:
list.append(node_dequeued.right)
print()
for node in list:
q.put(node)

# iteration version
def pre_order_iter(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> pre_order_iter(root)
1,2,4,5,3,6,7,
"""
if not isinstance(node, TreeNode) or not node:
return
stack: list[TreeNode] = []
n = node
while n or stack:
while n:  # start from root node, find its left child
print(n.data, end=",")
stack.append(n)
n = n.left
# end of while means current node doesn't have left child
n = stack.pop()
# start to traverse its right child
n = n.right

def in_order_iter(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> in_order_iter(root)
4,2,5,1,6,3,7,
"""
if not isinstance(node, TreeNode) or not node:
return
stack: list[TreeNode] = []
n = node
while n or stack:
while n:
stack.append(n)
n = n.left
n = stack.pop()
print(n.data, end=",")
n = n.right

def post_order_iter(node: TreeNode) -> None:
"""
>>> root = TreeNode(1)
>>> tree_node2 = TreeNode(2)
>>> tree_node3 = TreeNode(3)
>>> tree_node4 = TreeNode(4)
>>> tree_node5 = TreeNode(5)
>>> tree_node6 = TreeNode(6)
>>> tree_node7 = TreeNode(7)
>>> root.left, root.right = tree_node2, tree_node3
>>> tree_node2.left, tree_node2.right = tree_node4 , tree_node5
>>> tree_node3.left, tree_node3.right = tree_node6 , tree_node7
>>> post_order_iter(root)
4,5,2,6,7,3,1,
"""
if not isinstance(node, TreeNode) or not node:
return
stack1, stack2 = [], []
n = node
stack1.append(n)
while stack1:  # to find the reversed order of post order, store it in stack2
n = stack1.pop()
if n.left:
stack1.append(n.left)
if n.right:
stack1.append(n.right)
stack2.append(n)
while stack2:  # pop up from stack2 will be the post order
print(stack2.pop().data, end=",")

def prompt(s: str = "", width=50, char="*") -> str:
if not s:
return "\n" + width * char
left, extra = divmod(width - len(s) - 2, 2)
return f"{left * char} {s} {(left + extra) * char}"

if __name__ == "__main__":
import doctest

doctest.testmod()
print(prompt("Binary Tree Traversals"))

node = build_tree()
print(prompt("Pre Order Traversal"))
pre_order(node)
print(prompt() + "\n")

print(prompt("In Order Traversal"))
in_order(node)
print(prompt() + "\n")

print(prompt("Post Order Traversal"))
post_order(node)
print(prompt() + "\n")

print(prompt("Level Order Traversal"))
level_order(node)
print(prompt() + "\n")

print(prompt("Actual Level Order Traversal"))
level_order_actual(node)
print("*" * 50 + "\n")

print(prompt("Pre Order Traversal - Iteration Version"))
pre_order_iter(node)
print(prompt() + "\n")

print(prompt("In Order Traversal - Iteration Version"))
in_order_iter(node)
print(prompt() + "\n")

print(prompt("Post Order Traversal - Iteration Version"))
post_order_iter(node)
print(prompt())
```  