def fee_per_byte(self, network: 'Network') -> Optional[int]:
        """Returns sat/vB fee to pay for a txn.
        Note: might return None.
        """
        fee_per_kb = self.fee_per_kb(network)
        return fee_per_kb / 1000 if fee_per_kb is not None else None
Returns sat/vB fee to pay for a txn.
        Note: might return None.
        
electrum/fee_policy.py