code: def update(self, event=None, force=False):
          
          line_no = self.text.index(tkinter.INSERT).split(".")[0]
  
          # if not force:
              # if line_no == self.current_line:
  #                 log.critical("no highlight line needed.")
  #                 return
  
  #         log.critical("highlight line: %s" % line_no)
  #         self.current_line = line_no
  
          self.text.tag_remove(self.tag_current_line.id, "1.0", "end")
          self.text.tag_add(self.tag_current_line.id, "%s.0" % line_no, "%s.0+1lines" % line_no)
docs: highlight the current line