def data_to_output(sentences, write_to_file=''):
  """Convert data to a string of data stream that is ready to write

  Args:
      sentences (list): A list of sentences
      write_to_file (str, optional):
        If a file path, write data stream to that file

  Returns:
      output_list: A list of strings, each line indicating a line in file
  """
  output_list = []
  for sentence in sentences:
    for tup in sentence:
      output_list.append('\t'.join(tup))
    output_list.append('')
  if write_to_file:
    with open(write_to_file, 'w') as f:
      f.write('\n'.join(output_list))
  return output_list