code: def select_by_value(self, value):
          
          self._selected_key = None
          self._selected_item = None
          for k in self.children:
              item = self.children[k]
              if item.get_text() == value:
                  item.attributes['selected'] = 'selected'
                  self._selected_key = k
                  self._selected_item = item
              else:
                  if 'selected' in item.attributes:
                      del item.attributes['selected']
docs: Selects a DropDownItem by means of the contained text-
  
          Args:
              value (str): Textual content of the DropDownItem that have to be selected.