'Change the current standing offer. We leave it up to the
command to do the actual checks that the offer consists
of real, valid, objects.
Args:
party (object): Who is making the offer
args (objects or str): Offerings.'

def offer(self, party, *args):

    if self.trade_started:
        self.part_a_accepted = False
        self.part_b_accepted = False
        if (party == self.part_a):
            self.part_a_offers = list(args)
        elif (party == self.part_b):
            self.part_b_offers = list(args)
        else:
            raise ValueError
