input: 
  def dropLeafNodes(head): 
      """ Removes all leaf nodes from a given Huffman tree.
      >>> dropLeafNodes(None)
      None
      >>> dropLeafNodes(TreeNode(1, TreeNode(2, TreeNode(4), TreeNode(5)), TreeNode(3, TreeNode(6), TreeNode(7))))
      TreeNode(1, TreeNode(2, None, None), TreeNode(3, None, None))
      """
  
      # If node is not None and doesn't have any children 
      if head and not head.left and not head.right: 
          return None
    
      # Don't change anything if head is None 
      if not head: 
          return None
    
      # Recursively call dropLeafNodes on left and right subtrees
      head.left = dropLeafNodes(head.left) 
      head.right = dropLeafNodes(head.right) 
    
      # Return head of the modified tree
      return head
  
output:     # If node is not None and doesn't have any children 
      if head and not head.left and not head.right: 
          return None
    
      # Don't change anything if head is None 
      if not head: 
          return None
    
      # Recursively call dropLeafNodes on left and right subtrees
      head.left = dropLeafNodes(head.left) 
      head.right = dropLeafNodes(head.right) 
    
      # Return head of the modified tree
      return head