input: def dropLeafNodes(head): 
      """Remove all leaf nodes from a given Huffman tree.
  
      >>> class Node:
      ...     def __init__(self, value, left=None, right=None):
      ...         self.value = value
      ...         self.left = left
      ...         self.right = right
      ...
      >>> tree = Node(1, Node(2, Node(4), Node(5)), Node(3, Node(6), Node(7)))
      >>> result = dropLeafNodes(tree)
      >>> print(result.value)
      1
      >>> print(result.left.value)
      2
      >>> print(result.right.value)
      3
      >>> print(result.left.left)
      None
      >>> print(result.left.right)
      None
      >>> print(result.right.left)
      None
      >>> print(result.right.right)
      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