new_contents: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  
  class Node(object):
      pass
  
  
  class Trie(object):
      pass
  
  
  def main():
      pass
  
  if __name__ == '__main__':
      main()
  
subject: Add ds_trie.py