tree.py

from collections import deque


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

    def __str__(self):
        return f'[{self.key}, {self.left}, {self.right}]'

    def __repr__(self):
        return str(self)

t = Node( 'C', Node('F', Node('D')), Node('B', Node('A', Node('G'), Node('E'))))

def level_order(t):
    result =[]
    if t:
        d = deque()
        d.append(t)
        while len(d):
            n = d.popleft()
            result.append(n.key)
            if n.left:
                d.append(n.left)
            if n.right:
                d.append(n.right)
    return result

def preorder(t):
    result = []
    def f(n):
        if n:
            result.append(n.key)
            f(n.left)
            f(n.right)
    f(t)
    return result

def inorder(t):
    result = []
    def f(n):
        if n:

            f(n.left)
            result.append(n.key)
            f(n.right)
    f(t)
    return result

def postorder(t):
    result = []
    def f(n):
        if n:
            f(n.left)
            f(n.right)
            result.append(n.key)
    f(t)
    return result