code: def plot_item(self, funcname):
          
          index = self.currentIndex()
          if self.__prepare_plot():
              key = self.model.get_key(index)
              try:
                  self.plot(key, funcname)
              except (ValueError, TypeError) as error:
                  QMessageBox.critical(self, _( "Plot"),
                                       _("<b>Unable to plot data.</b>"
                                         "<br><br>Error message:<br>%s"
                                         ) % str(error))
docs: Plot item