binary tree in python

class :
    def __init__(self,size = 16):
        self.queue = []
        self.size = size
        self.front = 0
        self.rear = 0
    def is_empty(self):
        return self.rear == 0
    def is_full(self):
        if (self.front - self.rear +1) == self.size:
            return True
        else:
            return False
    def first(self):
        if self.isEmpty():
            raise Exception("QueueIsEmpty")
        else:
            return self.queue[self.front]
    def last(self):
        if self.isEmpty():
            raise Exception("QueueIsEmpty")
        else:
            return self.queue[self.rear]
    def add(self,obj):
        if self.isFull():
            raise Exception("QueueOverFlow")
        else:
            self.queue.append(obj)
            self.rear += 1
    def delete(self):
        if self.isEmpty():
            raise Exception("QueueIsEmpty")
        else:
            self.rear -=1
            return self.queue.pop(0)
    def show(self):
        print(self.queue)

class BinaryTreeNode:
    def __init__(self,data,left,right):
        self.left = left
        self.data = data
        self.right = right
class BinaryTree:
    def __init__(self):
        self.root = None
    def make_tree(self,data,left,right):
        self.root = BinaryTreeNode(data,left,right)
        
    def is_empty(self):
        if self.root is None:
            return True
        else:
            return False
    def pre_order(self,r):
        if r.root is not None:
            print(r.root.data)
            if r.root.left is not None:
                self.preOrder(r.root.left)
            if r.root.right is not None:
                self.preOrder(r.root.right)
    def in_order(self,r):
        if r.root is not None:
            if r.root.left is not None:
                self.inOrder(r.root.left)
            print(r.root.data)
            if r.root.right is not None:
                self.inOrder(r.root.right)
    def post_order(self,r):
        if r.root is not None:
            if r.root.left is not None:
                self.preOrder(r.root.left)
            if r.root.right is not None:
                self.preOrder(r.root.right)
            print(r.root.data)
    def level_order(self,a):
        q = Queue()
        r = a
        while r is not None:
            print(r.root.data)
            if r.root.left is not None:
                q.add(r.root.left)
            if r.root.right is not None:
                q.add(r.root.right)
            if q.isEmpty():
                print("empty")
                r = None
            else:
                r = q.delete()
    def invert_order(self, r):
        print(r.root.data)
        if r.root.left is not None and r.root.right is not None:
            r.root.left, r.root.right = r.root.right, r.root.left
            if r.root.left is not None:
                self.invertOrder(r.root.right)
            if r.root.right is not None:
                self.invertOrder(r.root.left)