Can someone help me with this PYTHON code!

In this notebook you will complete the following implementation of the balanced (AVL) binary search tree. Note that you should not be implementing the map-based API described in the plain (unbalanced) BSTree notebook i.e., nodes in the AVLTree will only contain a single value.

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class AVLTree: 

 class Node: 

 def __init__(self, val, left=None, right=None): 

 self.val = val 

 self.left = left 

 self.right = right 

 def rotate_right(self): 

 n = self.left 

 self.val, n.val = n.val, self.val 

 self.left, n.left, self.right, n.right = n.left, n.right, n, self.right 

 def rotate_left(self): 

 # YOUR CODE HERE 

 raise NotImplementedError() 

 @staticmethod 

 def height(n): 

 if not n: 

 return 0 

 else: 

 return max(1+AVLTree.Node.height(n.left), 1+AVLTree.Node.height(n.right)) 

 def __init__(self): 

 self.size = 0 

 self.root = None 

 @staticmethod 

 def rebalance(t): 

 # YOUR CODE HERE 

 raise NotImplementedError() 

 def add(self, val): 

 assert(val not in self) 

 # YOUR CODE HERE 

 raise NotImplementedError() 

 def __delitem__(self, val): 

 assert(val in self) 

 # YOUR CODE HERE 

 raise NotImplementedError() 

 def __contains__(self, val): 

 def contains_rec(node): 

 if not node: 

 return False 

 elif val < node.val: 

 return contains_rec(node.left) 

 elif val > node.val: 

 return contains_rec(node.right) 

 else: 

 return True 

 return contains_rec(self.root) 

 def __len__(self): 

 return self.size 

 def __iter__(self): 

 def iter_rec(node): 

 if node: 

 yield from iter_rec(node.left) 

 yield node.val 

 yield from iter_rec(node.right) 

 yield from iter_rec(self.root) 

 def pprint(self, width=64): 

 """Attempts to pretty-print this tree's contents.""" 

 height = self.height() 

 nodes = [(self.root, 0)] 

 prev_level = 0 

 repr_str = '' 

 while nodes: 

 n,level = nodes.pop(0) 

 if prev_level != level: 

 prev_level = level 

 repr_str += ' ' 

 if not n: 

 if level < height-1: 

 nodes.extend([(None, level+1), (None, level+1)]) 

 repr_str += '{val:^{width}}'.format(val='-', width=width//2**level) 

 elif n: 

 if n.left or level < height-1: 

 nodes.append((n.left, level+1)) 

 if n.right or level < height-1: 

 nodes.append((n.right, level+1)) 

 repr_str += '{val:^{width}}'.format(val=n.val, width=width//2**level) 

 print(repr_str) 

 def height(self): 

 """Returns the height of the longest branch of the tree.""" 

 def height_rec(t): 

 if not t: 

 return 0 

 else: 

 return max(1+height_rec(t.left), 1+height_rec(t.right)) 

 return height_rec(self.root)