code: def change_option(self, option_name, new_value):
          
          if option_name == 'dataframe_format':
              assert new_value.startswith('%')
              new_value = new_value[1:]
          self.sig_option_changed.emit(option_name, new_value)
docs: Change a config option.
  
          This function is called if sig_option_changed is received. If the
          option changed is the dataframe format, then the leading '%' character
          is stripped (because it can't be stored in the user config). Then,
          the signal is emitted again, so that the new value is saved in the
          user config.