python基础:三层循环

三层循环基本演示:

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

文件内容查找和替换:

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()
‘‘‘

购物车基本演示:

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