code: def lines(text):
      
      assert text is not None
      assert '\r' not in text
      previous_newline_index = 0
      newline_index = text.find('\n')
      while newline_index != -1:
          yield text[previous_newline_index:newline_index]
          previous_newline_index = newline_index + 1
          newline_index = text.find('\n', previous_newline_index)
      last_line = text[previous_newline_index:]
      if last_line != '':
          yield last_line
docs: Generator function to yield lines (delimited with ``'\n'``) stored in
      ``text``. This is useful when a regular expression should only match on a
      per line basis in a memory efficient way.