Getting AttributeError: 'NoneType' object has no attribute 'rightnode' in avl tree

I am currently learning data structures and I have having an issue in AVL tree.

Code:

from myqueue import Queue   # my custom queue implemented by linked list

class AVL:

    def __init__(self,data):
        self.data=data
        self.leftnode=self.rightnode=None
        self.height=1

    def LevelOrderTransversal(self):
        if not self:
            return 
        queue=Queue()
        queue.enqueue(self)
        while not (queue.isempty()):
            root=queue.dequeue()
            print(root.data)
            if root.leftnode is not None:
                queue.enqueue(root.leftnode)
            if root.rightnode is not None:
                queue.enqueue(root.rightnode)

def getheight(rootnode):
    if not rootnode:
        return 0
    return rootnode.height

def getbalance(rootnode):
    if not rootnode:
        return 0
    return getheight(rootnode.leftnode)-getheight(rootnode.rightnode)

def leftrotation(disbalancenode):
    rootnode=disbalancenode.rightnode
    disbalancenode.rightnode=disbalancenode.rightnode.leftnode
    rootnode.leftnode=disbalancenode
    disbalancenode.height=1+max(getheight(disbalancenode.leftnode),getheight(disbalancenode.rightnode))
    rootnode.height=1+max(getheight(rootnode.leftnode),getheight(rootnode.rightnode))
    return rootnode

def rightrotation(disbalancenode):
    rootnode=disbalancenode.leftnode
    disbalancenode.leftnode=disbalancenode.leftnode.rightnode
    rootnode.rightnode=disbalancenode
    disbalancenode.height=1+max(getheight(disbalancenode.leftnode),getheight(disbalancenode.rightnode))
    rootnode.height=1+max(getheight(rootnode.leftnode),getheight(rootnode.rightnode))
    return rootnode

def insertnode(rootnode,nodevalue):
    if rootnode.data is None:
        return AVL(nodevalue)
    elif nodevalue<rootnode.data:
        if rootnode.leftnode is None:
            rootnode.leftnode=AVL(nodevalue)
        else:
            insertnode(rootnode.leftnode,nodevalue)
    else:
        if rootnode.rightnode is None:
            rootnode.rightnode=AVL(nodevalue)
        else:
            insertnode(rootnode.rightnode,nodevalue)

    rootnode.height=1+max(getheight(rootnode.leftnode),getheight(rootnode.rightnode))
    balance=getbalance(rootnode)
    
    if balance>1 and nodevalue<rootnode.leftnode.data:
        return rightrotation(rootnode)
    if balance>1 and nodevalue>rootnode.leftnode.data:
        rootnode.leftnode=leftrotation(rootnode.leftnode)
        return rightrotation(rootnode)
    if balance<-1 and nodevalue<rootnode.rightnode.data:
        return leftrotation(rootnode)
    if balance<-1 and nodevalue>rootnode.rightnode.data:
        rootnode.rightnode=rightrotation(rootnode.rightnode)
        return leftrotation(rootnode)
    return rootnode



A=AVL(5)
A=insertnode(A,10)
A=insertnode(A,15)
A=insertnode(A,20)
A.LevelOrderTransversal()

Since the leftnode is disbalanced so it's raising error in rightrotation() method when we try to balance that node

So the error is arising in insertnode() method

Error I am getting:

Traceback (most recent call last):
  File "c:\Users\Anurag Dabas\Desktop\python\avl tree\newavl.py", line 84, in <module>     
    A=insertnode(A,15)
  File "c:\Users\Anurag Dabas\Desktop\python\avl tree\newavl.py", line 76, in insertnode   
    rootnode.rightnode=rightrotation(rootnode.rightnode)
  File "c:\Users\Anurag Dabas\Desktop\python\avl tree\newavl.py", line 45, in rightrotation
    disbalancenode.leftnode=disbalancenode.leftnode.rightnode
AttributeError: 'NoneType' object has no attribute 'rightnode'

I tried debugging but couldn't found anything

Here is my myqueue.py file: https://paste-bin.xyz/18851

Any help or clue will be appreciated

Thanks

Edit:

currently my tree looks like:

  5
   \
   10
     \  
      15
       \
        20
 #as you can see it's clearly unbalance so we need leftrotation since it's RR condition

so after doing left rotation result looks like:

Solution

There are actually several reasons why you get this error:

The balance factor is calculated in the opposite sense than it is commonly done: your balance factor will be positive when the tree has a higher left subtree, and negative when it has a higher right subtree. This is confusing to me.
Possibly you had the same confusion, because the comparison operators in the multiple if conditions (like: nodevalue<rootnode.leftnode.data) are in the wrong sense, and so your code ended up doing the wrong rotation, leading to the exception.
When you do a double rotation, then the rotations should be opposite in direction. In one case you have two consecutive leftrotation calls. That is wrong.

So without changing the balance calculation, you would correct it with:

    rootnode.height=1+max(getheight(rootnode.leftnode),getheight(rootnode.rightnode))
    balance=getbalance(rootnode)
    if balance>1 and nodevalue<rootnode.leftnode.data:
        return rightrotation(rootnode)
    if balance>1 and nodevalue>rootnode.leftnode.data:
        rootnode.leftnode=leftrotation(rootnode.leftnode)
        return rightrotation(rootnode)  # <-- corrected
    if balance<-1 and nodevalue>rootnode.rightnode.data:
        return leftrotation(rootnode)
    if balance<-1 and nodevalue<rootnode.rightnode.data:
        rootnode.rightnode=rightrotation(rootnode.rightnode)
        return leftrotation(rootnode)
    return rootnode