Python基础-小程序练习（跳出多层循环，购物车，多级菜单，用户登录）

一、 从第3层循环直接跳出所有循环

break_flag = False
count = 0
while break_flag == False:
    print("-第一层")
    while break_flag == False:
        print("第二层")
        while break_flag == False:
            count += 1
            if count > 10:
                break_flag = True
            print("第三层")
print("keep going...")

with break_flag

# break_flag = False
count = 0
while count < 3:
    print("-第一层")
    while count < 3:
        print("第二层")
        while count <= 10:
            count += 1
            # if count > 10:
            #     break_flag = True
            print("第三层")
print("keep going...")

without break_flag

二、 购物车程序

goods_list = [['Iphone7',5800],['Coffee',30],['Book',99],['Bike',199],['Vivi X9',2499]]     #商品列表
shopping_cart = []      #用户购物车列表
salary = int(input('input your salary:'))       #用户薪水
m = salary
k = 0

while True:
    index = 0
    for goods in goods_list:        #打印商品列表
        print(index,goods)
        index += 1
    choice = input('>>>:').strip()
    if choice.isdigit():
        choice = int(choice)
        if choice >= 0 and choice < len(goods_list):
            goods = goods_list[choice]
            if goods[1] <= salary:      #判断用户是否带了足够的钱来支付所选商品
                shopping_cart.append(goods)
                salary -= goods[1]
                print('Add goods '+str(goods[0])+' into shopping cart! Your current balance:'+str(salary))
            else:
                print('No enough money!The price is:'+str(goods[1])+'! Need more:'+str(goods[1]-salary))
        else:
            print('Have no this goods!')
    elif choice == 'q':
        print('----------Your shopping cart----------')
        print('ID   goods   quantity    price   total')
        for i in range(len(goods_list)):
            j = shopping_cart.count(goods_list[i])
            if j > 0 :
                k += 1
                print(k,'\t',goods_list[i][0],'\t',j,'\t\t',goods_list[i][1],'\t',j * goods_list[i][1])

        print('Total price is:',m - salary)
        break
    else:
        print('Have no this goods')

购物车程序

goods_list = [['Iphone7',5800],['Coffee',30],['Book',99],['Bike',199],['Vivi X9',2499]]  # 商品列表
shopping_cart = {}  # 用户购物车列表从列表变为字典
salary = int(input('input your salary:'))  # 用户薪水
# m = salary #不需要此项
# k = 0 #用户购物车商品打印ID，移动位置至打印循环外

while True:
    index = 0
    for goods in goods_list:  # 打印商品列表
        print(index, goods)
        index += 1
    choice = input('>>>:').strip()
    if choice.isdigit():  # 判断是否为数字
        choice = int(choice)
        if choice >= 0 and choice < len(goods_list):  # 商品存在
            goods = goods_list[choice]
            if goods[1] <= salary:  # 判断用户是否带了足够的钱来支付所选商品
                if goods[0] in shopping_cart:  # 之前买过
                    shopping_cart[goods[0]][1] += 1  # 购物数量加1
                else:
                    shopping_cart[goods[0]] = [goods[1], 1]  # 创建一条新增商品的购买记录
                salary -= goods[1]  # 扣钱
                print('Add goods ' + str(goods[0]) + ' into shopping cart! Your current balance:' + str(salary))
            else:
                print('No enough money!The price is:' + str(goods[1]) + '! Need more:' + str(goods[1] - salary))
        else:
            print('Have no this goods!')
    elif choice == 'q':
        id_counter = 1  # 初始化商品ID
        total_cost = 0  # 初始化商品总花费
        print('----------Your shopping cart----------')
        print('ID   goods     quantity    price     total')
        for i in shopping_cart:
            print("%-5s%-10s%-12s%-10s%-s"
                  % (
                      id_counter, i, shopping_cart[i][1], shopping_cart[i][0],
                      shopping_cart[i][0] * shopping_cart[i][1]))
            id_counter += 1  # 商品ID自加1
            total_cost += shopping_cart[i][0] * shopping_cart[i][1]  # 用户已购商品总花费
        print('Total price is:', total_cost)
        break
    else:
        print('Have no this goods')

购物车程序优化，使用字典

三、多级菜单

要求:

1. 打印省、市、县三级菜单
2. 可返回上一级（b，返回）
3. 可随时退出程序（q，退出）

menu = {
    '北京':{
        '海淀':{
            '五道口':{
                'soho':{},
                '网易':{},
                'google':{}
            },
            '中关村':{
                '爱奇艺':{},
                '汽车之家':{},
                'youku':{},
            },
            '上地':{
                '百度':{},
            },
        },
        '昌平':{
            '沙河':{
                '老男孩':{},
                '北航':{},
            },
            '天通苑':{},
            '回龙观':{},
        },
        '朝阳':{},
        '东城':{},
    },
    '上海':{
        '闵行':{
            "人民广场":{
                '炸鸡店':{}
            }
        },
        '闸北':{
            '火车战':{
                '携程':{}
            }
        },
        '浦东':{},
    },
    '山东':{},
}

exit_flag = False
current_layer = menu

layers = [menu]

while not exit_flag:
    for k in current_layer:
        print(k)
    choice = input(">>:").strip()
    if choice == "b":
        current_layer = layers[-1]
        #print("change to laster", current_layer)
        layers.pop()
    elif choice == 'q':
        break
    elif choice not in current_layer:
        continue
    else:
        layers.append(current_layer)
        current_layer = current_layer[choice]

四、用户登陆程序

需求：

1. 最多允许用户尝试登陆3次
2. 当同一用户名3次密码均不正确时，锁定该用户

 with open('account',encoding='utf8') as f_account, open('lockedlist', 'a+') as f_locked:
     l = []                  #定义用户名验证列表，存放黑名单数据
     f_locked.seek(0)        #"a+"模式打开后，文件位置位于末尾，要遍历文件内容，需要将指针移至文件起始位置
     for locked_info in f_locked.readlines():    #遍历黑名单
         l.append(locked_info.strip())                   #将黑名单数据添加进列表,注意：需要将文件中的换行符脱掉

     c = []                  #定义用户登录名列表，存储用户尝试的登录名
     count = 1               #登陆次数计数器
     flag = True             #登陆循环控制开关
     while flag and count < 4:
         user = input('Please input username:')      #输入用户名
         pwd = input('Please input password:')       #输入用户密码
         if user in l:                 #用户名在黑名单中
             print("This user is in blacklist,can't log in!")    #打印提示信息
             continue
         c.append(user)
         for info in f_account:                  #用户名不在黑名单中，遍历用户登陆文件
             user_name, user_pwd = info.strip().split(',')       #将文件中的用户名和登陆密码赋值给判定变量
             if user == user_name:               #用户名符合
                 if pwd == user_pwd:             #对应密码符合
                     print('Welcome %s' % user)  #打印登陆成功信息
                     flag = False               #登陆成功，跳出登陆程序
                     break
                 count += 1                      #对应密码不符合，while循环计数器加1
                 break
             count += 1                          #用户名不符合，while循环计数器加1
             break
     if count == 4:                              #如果不同用户名密码输错3次，关闭程序
         print('More than 3 times wrong!')       #打印提示信息
     if len(c) == 3 and c[0] == c[1] == c[2]:    #如果相同用户名密码输错3次，将该用户名加入黑名单，限制登陆
         print('This user has been locked!')
         f_locked.write(user+'\n')               #将错误3次的用户名写入黑名单，注意，加换行符

用户登陆程序