编写程序对文件进行增删改查

import os
def fetch(data):
    print('\033[1;41m这是查询功能\033[0m')
    print('\033[1;41m用户数据\033[0m', data)
    backend_data = 'backend %s' %data
    with open ('lala.conf', 'r', encoding = 'utf-8') as read_f:
        tag = False
        ret = []

        for read_line in read_f:
            if read_line.strip() == backend_data:
                tag = True
                continue
            if tag and read_line.startswith('backend'):
                break
            if tag:

                ret.append(read_line)

    return ret

def add():
    pass

def change(data):
    print("这是修改功能")
    backend = data[0]['backend']   #文件中的一条记录 www.oldboy1.org
    backend_data = 'backend %s' %backend

    old_service_recode = '%sservice %s %s weight %s maxconn %s\n' % (' '*8,data[0]['record']['service'],
                                                                     data[0]['record']['service'],
                                                                     data[0]['record']['weight'],
                                                                     data[0]['record']['maxconn'])

    new_service_recode = '%sservice %s %s weight %s maxconn %s\n' % (' ' * 8, data[1]['record']['service'],
                                                                     data[1]['record']['service'],
                                                                     data[1]['record']['weight'],
                                                                     data[1]['record']['maxconn'])
    print('用户想要修改的记录是%s' % old_service_recode)
    res = fetch(backend)
    if not res or old_service_recode not in res:
        return '你要修改的文件不存在'
    else:
        index1 = res.index(old_service_recode)
        res[index1] = new_service_recode
    res.insert(0, '%s\n'%backend_data)

    with open('lala.conf', 'r', encoding='utf-8') as read_f, open('lala_new.conf', 'w', encoding = 'utf8') as write_f:
        tag = False
        has_write = False
        for read_line in read_f:

            if read_line.strip() == backend_data:
                tag = True
                continue
            if tag and read_line.startswith('backend'):
                tag = False
            if not tag:
                write_f.write(read_line)
            else:
                if not has_write:
                    for record in res:
                        write_f.write(record)
                    has_write = True
    os.rename('lala.conf', 'sb')
    os.rename('lala_new.conf', 'lala.conf')
    os.remove('sb')







def delete():
    pass

if __name__ == '__main__':
    msg = '''
    1: 查询
    2: 添加
    3: 修改
    4: 删除
    5: 退出
    '''
    msg_dic = {
        '1': fetch,
        '2': add,
        '3': change,
        '4': delete
    }

    while True:
        print(msg)
        choice = input('请输入你的选项:').strip()
        if not choice:continue  #如果输入为空或者回车，将重新输入
        if choice == '5': break

        data = input('请输入你的数据：').strip()
        if choice != '1':
            data = eval(data)

        res = msg_dic[choice](data)
        print(res)

　　数据输入：[{'backend':'www.oldboy1.org', 'record': {'service':'2.2.2.4','weight':20,'maxconn':30000}},{'backend':'www.oldboy1.org','record': {'service':'2.2.2.5','weight':30,'maxconn':4000}}]