break_flag = False                                                     #标记1

break_flag2 = False                                                    #标记2

break_flag3 = False                                                    #标记3

while not break_flag:                                                  #因为标记是False,所以是 not break_flag成立循环

    print("the first layer is running...")

    option=input(">>>[b:back, q:quit,c:continue]:").strip()            #让买家选择,strip()去除输入时空格

    if option == "b":

        break_flag2 = True                                             #第一层,没得退,所以break_flag2=true,不断打印'the first...'

    elif option == "q":

        break_flag = True                                              #选择退出,把循环条件改为true,就能退出循环

    else:

        break_flag3,break_flag2 = False,False                          #既不是b,也不是q,则第二三层循环条件继续成立,往下走

    while not (break_flag or break_flag2):                             #进入第二层,那么第一层循环条件必须是false,q时随时可以退出

        print("in layer two...")

        option=input(">>>[b:back, q:quit,c:continue]:").strip()

        if option == "b":

            break_flag2 = True                                         #退到第一层,因为else:break_flag3,break_flag2 = False,False

        elif option == "q":

            break_flag = True                                          #退出整个循环

        else:

            break_flag2,break_flag3 = False,False                      #这里可以实现第二层第三层的切换

        while not(break_flag or break_flag2 or break_flag3):           #与上面同理

            print("in layer three...")

            option=input(">>>[b:back, q:quit,c:continue]:").strip()

            if option == "b":

                break_flag3 = True

            elif option == "q":

                break_flag = True

import os                                                       #os操作系统模块

f = open("test.txt","r")                                        #旧文件读模式

f_new = open("text_new.txt","w")                                #新文件写模式

for line in f:                                                  #遍历旧文件

    if line.startswith("alex"):                                 #找到要替换的行

        new_line = line.replace("alex","ALEX LI....")           #替换好赋值给新行

        f_new.write(new_line)                                   #把新行写到新文件

    else:

        f_new.write(line)                                       #如果找不到,则把原文写到新文件

f.close()

f_new.close()

os.rename("test.txt","test.txt.bak")                            #把旧文件改名为back up

os.rename("text_new.txt","test.txt")                            #新文件覆盖旧文件

'''

f = open("test.txt","r+")

for line in f:

    if line.startswith("alex"):

        new_line = line.replace("alex","ALEX LI")

        print("current pos:",f.tell())                          #显示指针的位置

        f.seek(37)                                              #把指针指到该位置

        f.write(new_line)

        break

f.close()

'''

product_list = [

    ('Iphone6sPlus', 6888),

    ('MacBook', 11300),

    ('CookBook', 50),

    ('Coffee', 30),

    ('KindleFire', 1200),

    ('NB', 800),

]

user_asset = 10000

break_flag = False

shopping_cart = []

paid_list = []

while not break_flag:

    for index,i in enumerate(product_list):

        print(index,i[0],i[1])

    user_choice = raw_input("[quit,check,pay]What do you want to buy?:").strip()

    if user_choice.isdigit():

        user_choice = int(user_choice)

        if user_choice < len(product_list) and user_choice > -1:

            shopping_cart.append(product_list[user_choice])

            print("\033[32;1mJust added [%s,%s] in to your shopping cart\033[0m" %(product_list[user_choice]))

        else:

            print("\033[31;1mProduct [%s] is not exist!\033[0m")

    elif user_choice == "check":

        total_price = 0

        print("\033[34;1mYou have bought below products...:\033[0m")

        for index,p in enumerate(shopping_cart):

            print(index,p)

            total_price += p[1]

        print("Total Price:\033[31;1m[%s]\033[0m" % total_price)

    elif user_choice == "pay":

        total_price = 0

        print("\033[34;1mYou have bought below products...:\033[0m")

        for index,p in enumerate(shopping_cart):

            print(index,p)

            total_price += p[1]

        print("Total Price:\033[31;1m[%s]\033[0m" % total_price)

        pay_confirm = raw_input("\033[31;1mGoing to pay?\033[0m").strip()

        if pay_confirm == "y":

            money_left = user_asset - total_price

            if money_left > 0:

                paid_list += shopping_cart

                shopping_cart = []

                user_asset = money_left

                print("\033[31;1mYou have just paid[%s], your current balance is [%s]\033[0m" %(total_price,money_left))

                go_confirm = raw_input("press any key to continue shopping!").strip()

            else:

                print("\033[31;1mYour current balance is [%s], still need [%s] to pay the whole deal!\033[0m" %(user_asset,total_price-user_asset))

    elif user_choice == "quit":

        if shopping_cart:

            print("You still have some product haven't paid yet!")

        else:

            print("Thanks for comming!")

            break_flag = True