input: def dropLeafNodes(head): 
      """Drops all the leaf nodes in the given Huffman tree.
  
      >>> dropLeafNodes({'val': 1, 'left': {'val': 2, 'left': {'val': 4, 'left': None, 'right': None}, 'right': {'val': 5, 'left': None, 'right': None}}, 'right': {'val': 3, 'left': {'val': 6, 'left': None, 'right': None}, 'right': {'val': 7, 'left': None, 'right': None}}})
      {'val': 1, 'left': {'val': 2, 'left': None, 'right': None}, 'right': {'val': 3, 'left': None, 'right': None}}
      >>> dropLeafNodes({'val': 1, 'left': None, 'right': 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
  