code: def num_empty(root):
      if root is None:
          return 1
      elif root.left is None and root.right:
          return 1 + num_empty(root.right)
      elif root.right is None and root.left:
          return 1 + num_empty(root.left)
      else:
          return num_empty(root.left) + num_empty(root.right)
  
file_path: keon-algos/algorithms/tree/bst/num_empty.py
imports: import unittest
  from bst import Node
  from bst import bst
label_desc: Use image node_id 1 for calling a global function with example usage: num_empty(root) and returns: int, unknown, unknown, unknown