def register_account(self, account, portfolio_cookie=None):
        '''
        注册一个account到portfolio组合中
        account 也可以是一个策略类，实现其 on_bar 方法
        :param account: 被注册的account
        :return:
        '''
        # 查找 portfolio
        if len(self.portfolio_list.keys()) < 1:
            po = self.new_portfolio()
        elif portfolio_cookie is not None:
            po = self.portfolio_list[portfolio_cookie]
        else:
            po = list(self.portfolio_list.values())[0]
        # 把account 添加到 portfolio中去
        po.add_account(account)
        return (po, account)