code: def aggregations(self):
          
  
          prev_month_start = get_prev_month(self.end,
                                            self.closed.query.interval_)
          self.closed.query.since(prev_month_start,
                                  field="closed_at")
          closed_agg = self.closed.aggregations()
          self.opened.query.since(prev_month_start)
          opened_agg = self.opened.aggregations()
          if opened_agg == 0:
              bmi = 1.0  # if no submitted issues/prs, bmi is at 100%
          else:
              bmi = closed_agg / opened_agg
          return bmi
docs: Get the aggregation value for BMI with respect to the previous
          time interval.