how to swap two nodes in binary tree python

# Python program to swap nodes 
  
# A binary tree node 
class Node: 
  
    # constructor to create a new node   
    def __init__(self, data): 
        self.data = data 
        self.left = None
        self.right = None
  
# A utility function swap left node and right node of tree 
# of every k'th level  
def swapEveryKLevelUtil(root, level, k): 
      
    # Base Case  
    if (root is None or (root.left is None and
                        root.right is None ) ): 
        return 
  
    # If current level+1 is present in swap vector 
    # then we swap left and right node 
    if (level+1)%k == 0: 
        root.left, root.right = root.right, root.left 
      
    # Recur for left and right subtree 
    swapEveryKLevelUtil(root.left, level+1, k) 
    swapEveryKLevelUtil(root.right, level+1, k) 
  
      
# This function mainly calls recursive function 
# swapEveryKLevelUtil 
def swapEveryKLevel(root, k): 
      
    # Call swapEveryKLevelUtil function with  
    # initial level as 1 
    swapEveryKLevelUtil(root, 1, k) 
  
# Method to find the inorder tree travesal 
def inorder(root): 
      
    # Base Case 
    if root is None: 
        return 
    inorder(root.left) 
    print root.data,  
    inorder(root.right) 
  
# Driver code 
""" 
          1 
        /   \ 
       2     3 
     /      /  \ 
    4      7    8  
"""
root = Node(1) 
root.left = Node(2) 
root.right = Node(3) 
root.left.left = Node(4) 
root.right.right = Node(8) 
root.right.left = Node(7) 
  
k = 2 
print "Before swap node :" 
inorder(root) 
  
swapEveryKLevel(root, k) 
  
print "\nAfter swap Node : "
inorder(root) 
  
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)