code: def comment_lines(lines):
      
      ret = []
      for line in lines:
          ws_prefix, rest, ignore = RE_LINE_SPLITTER_COMMENT.match(line).groups()
          ret.append(ws_prefix + '#' + rest)
      return ''.join(ret)
docs: Comment out the given list of lines and return them.  The hash mark will
      be inserted before the first non-whitespace character on each line.