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.

def cost(self):
        """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.
        """
        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