code: def NetworkFee(self):
          
          if self._network_fee is None:
  
              input = Fixed8(0)
  
              for coin_ref in self.References.values():
                  if coin_ref.AssetId == GetBlockchain().SystemCoin().Hash:
                      input = input + coin_ref.Value
  
              output = Fixed8(0)
  
              for tx_output in self.outputs:
                  if tx_output.AssetId == GetBlockchain().SystemCoin().Hash:
                      output = output + tx_output.Value
  
              self._network_fee = input - output - self.SystemFee()
  
          #            logger.info("Determined network fee to be %s " % (self.__network_fee.value))
  
          return self._network_fee
docs: Get the network fee.
  
          Returns:
              Fixed8: