code: def selected_fields(self):
          
          items = self.lstFields.selectedItems()
          if items and self.mode == MULTI_MODE:
              return [item.text() for item in items]
          elif items and self.mode == SINGLE_MODE:
              return items[0].text()
          else:
              return []
docs: Obtain the fields selected by user.
  
          :returns: Keyword of the selected field.
          :rtype: list, str