Plot item

def plot_item(self, funcname):
        """Plot item"""
        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))