Python写存取款记录

import os
import pickle
import time

def save(fname):
    amount = int(input('金额: '))
    comment = input('备注: ')
    date = time.strftime('%Y-%m-%d')
    # 从文件中取出全部记录
    with open(fname, 'rb') as fobj:
        records = pickle.load(fobj)
    # 计算最新余额
    balance = records[-1][-2] + amount
    record = [date, amount, 0, balance, comment]
    records.append(record)
    # 把更新后的列表再次存入文件