def _calculate(self, startingPercentage, endPercentage, startDate, endDate):
        # get the defined subset of error values
        errorValues = self._get_error_values(startingPercentage, endPercentage, startDate, endDate)

        return float(sum(errorValues)) / float(len(errorValues))
Generate a unique key for a node.
dataset/ETHPy150Open T-002/pycast/pycast/errors/symmetricmeanabsolutepercentageerror.py/SymmetricMeanAbsolutePercentageError._calculate--crossover with--dataset/ETHPy150Open enthought/pyface/pyface/tree/node_tree_model.py/NodeTreeModel.get_key