code: def charges_net_effect(self):
          
          return Decimal(sum([charge.charge_value for charge in self.charges.values()
                              if charge.net_affecting]))
docs: The total effect of the net_affecting charges (note affect vs effect here).
  
          Currently this is single currency only (AMAAS-110).
  
          Cast to Decimal in case the result is zero (no net_affecting charges).
  
          :return: