code: def cost(self):
          
          total = 0.0
          for family, rules in self._excludes.iteritems():
              cost = sum(x.cost() for x in rules)
              if family:
                  cost = cost / float(10)
              total += cost
          return total
docs: Get the approximate cost of this filter.
  
          Cost is the total cost of the exclusion rules in this filter. The cost
          of family-specific filters is divided by 10.
  
          Returns:
              float: The approximate cost of the filter.