'This is used once B decides to join the trade
Args:
part_b (object): The party accepting the barter.'

def join(self, part_b):

    if (self.part_b == part_b):
        self.part_b.ndb.tradehandler = self
        self.part_b.cmdset.add(CmdsetTrade())
        self.trade_started = True
        return True
    return False
