def previous(self, step=1):
        ip_copy = self.__class__('%s/%d' % (self.network, self.prefixlen),
            self._module.version)
        ip_copy -= step
        return ip_copy
Take the (col, value) in 'values', append value into 'col' in self.data[]
dataset/ETHPy150Open drkjam/netaddr/netaddr/ip/__init__.py/IPNetwork.previous--crossover with--dataset/ETHPy150Open linkedin/naarad/src/naarad/metrics/top_metric.py/TopMetric.put_values_into_data