需求
用户登陆，第一次登陆，要求输入工资，商品信息从文件里读取，购买商品，扣除余额，退出之后，下一次登陆仍然记住余额；商家登陆，可以添加商品，修改商品价格。
思路
商品信息存放在文件里，程序启动时读取文件，将文件中的商品信息，组成列表。文件信息可以写成列表元组形式，也可以写成字符，再由程序拼接成列表元组，看实际操作怎么方便吧。
第一次登陆需要输入工资，之后就不需要，这个需要创建一个余额文件，启动程序读取文件，如果文件为空，则需要输入工资，如果不为空，读取余额文件，购买商品扣除余额之后修改余额文件。
添加商品，需要输入商品名，价格，创建一个列表，修改价格，用操作列表方式修改。
用户接口流程图
shopping.png
我们先做一个初步的程序，将列表直接写在脚本中，代码示例如下：
#-*- coding:utf-8 -*-
#owner:houyizhong
shoplist=[[1,"iphone",5800],[2,"ipad",3500],[3,"mac pro",12000],[4,"mac air",6800],[5,"apple watch",3000]]
my_shoplist=[]
salary=int(input("Enter your salary:"))
while True:
print(shoplist)
enter_choice=input("Enter your choice:")
#print enter_choice
#print type(enter_choice)
if enter_choice == "q":
print("your salary is {}".format(salary))
print("your shoplist is {}".format(my_shoplist))
break
else:
shop_choice=int(enter_choice)
i=shop_choice-1
shop_goods=shoplist[i][1]
price=shoplist[i][2]
if salary >= price:
print("you buy {}".format(shoplist[i]))
my_shoplist.append(shop_goods)
salary -= price
else:
print("\nsorry your salary isn's enought\n")
上面中，我们将商品列表写为
shoplist=[[1,"iphone",5800],[2,"ipad",3500],[3,"mac pro",12000],[4,"mac air",6800],[5,"apple watch",3000]]
也是说，每个商品的序号是写死的，这样是因为还未掌握打印列表项目序号的方法，通过学习和上网查找，我们知道，enumerate(list)方法可以打印出列表各项object的在列表中的index位置，用法如下：
list=["a","b","c"]
for i in enumerate(list):
print(i)
-----------------
(0, 'a')
(1, 'b')
(2, 'c')
另外，我们这个程序还有个bug就是，如果用户输入的"salary"和"enter_choice"既非数字也非退出键"q"，那么程序会出现报错，所以，我们需要对用户输入的salary和enter_choice做一个判断，我们用arg.isdigit()方法来判断变量是否是数字类型，用法示例如下（需要注意的是，变量赋值得是字符str，数字int是不能用isdigit方法判断的）：
salary=input()
if salary.isdigit():
print True
除此之外，我们还要考虑到当商品编号超出可供选择的范围会报错，所以我们还需要对用户输入的choice做一个判断如果，选择在0到5之间就返回正确的值，不在这个返回就会返回商品不存在信息。
经过完善，我们的代码如下：
#-*- coding:utf-8 -*-
#owner:houyizhong
shoplist=[["iphone",5800],["ipad",3500],["mac pro",12000],["mac air",6800],["apple watch",3000]]
my_shoplist=[]
salary=input("Enter your salary:")
if salary.isdigit():
salary=int(salary)
while True:
for index,item in enumerate(product_list):
print(index+1,item)
user_choice=input("Choice a product code:")
if user_choice.isdigit():
user_choice = int(user_choice)
if user_choice <= len(product_list) and user_choice > 0:
user_choice -= 1
if product_list[user_choice][1] <= salary:
shopping_list.append(product_list[user_choice][0])
salary -= product_list[user_choice][1]
print("Added {0} to your shopping_list!Your salary is {1}\n".format(product_list[user_choice][0],salary))
else:
print("Sorry your salary is not enought!\n")
else:
print("Sorry,product code isn's exist!\n")
elif user_choice == "q":
exit("Your shopping list is {0},your salary is {1}.".format(shopping_list,salary))
else:
print("Your enter invalid!\n")
else:
if salary == "q":
exit("Your shopping list is {0},your salary is {1}.".format(shopping_list,salary))
else:
print("Sorry,your enter invalid!")
继续
目前，我们已经做出了一个demo版的购物车程序，接下来，我们要实现从文件中读取数据。
根据以往的经验，我决定把存放商品信息的文件，按如下格式写：
#cat product.txt
iphone:5800
mac pro:12000
bike:800
book:55
coffee:31
这样我将信息加入列表时，就只需要按照":"来分裂原本并在一起的数据，用split(":")方法即可形成一个单独的小列表。
product_list=[['iphone', 5800], ['mac pro', 12000], ['bike', 800], ['book', 55], ['coffee', 31]]
问题
在实现过程中，遇到了一个问题，就是我从balance.txt文件中读取数据，file.readlines()形成一个列表，如果文件为空，则，这个列表为空，那么怎么判断列表是否为空呢，通过上网查询，很快找到了答案：
有两种方法，一种是根据len(list)来判断，另外一种直接以list为判断条件，list为空直接返回False，示例如下
if len(mylist):
# Do something with my list
else:
# The list is empty
if mylist:
# Do something with my list
else:
# The list is empty
两种方法都可以用来判断列表是否有数据。
形成代码如下：
product_list=[]
shopping_list=[]
#read product file
product_file=open("product.txt","r")
pro_read=product_file.readlines()
product_file.close()
#read product and price
for i in pro_read:
i=i.strip()
pro_raw=i.split(":")
price=int(pro_raw[1])
pro_raw.insert(1,price)
pro_raw.pop()
product_list.append(pro_raw)
#read balance file
balance_file=open("balance.txt","r")
bal_read=balance_file.readlines()
balance_file.close()
#if balance exists
if bal_read:
salary=int(bal_read)
else:
salary=input("Enter your salary:")
if salary.isdigit():
salary=int(salary)
while True:
for index,item in enumerate(product_list):
print(index+1,item)
user_choice=input("Choice a product code:")
if user_choice.isdigit():
user_choice = int(user_choice)
if user_choice <= len(product_list) and user_choice > 0:
user_choice -= 1
if product_list[user_choice][1] <= salary:
shopping_list.append(product_list[user_choice][0])
salary -= product_list[user_choice][1]
print("Added {0} to your shopping_list!Your salary is {1}\n".format(product_list[user_choice][0],salary))
else:
print("Sorry your salary is not enought!\n")
else:
print("Sorry,product code isn's exist!\n")
elif user_choice == "q":
exit("Your shopping list is {0},your salary is {1}.".format(shopping_list,salary))
else:
print("Your enter invalid!\n")
else:
if salary == "q":
exit("Your shopping list is {0},your salary is {1}.".format(shopping_list,salary))
else:
print("Sorry,your enter invalid!")
写入balance.txt
接下来，我们需要把余额写入balance文件，根据流程图，写入动作是发生在退出程序时的，每一次退出都要有修改文件的动作。所以我们用def函数来做这个操作更好。
代码如下：
#-*-coding:utf-8 -*-
#owner:houyizhong
#version:2.0
product_list=[]
shopping_list=[]
#read product file
product_file=open("product.txt","r")
pro_read=product_file.readlines()
product_file.close()
#read product and price
for i in pro_read:
i=i.strip()
pro_raw=i.split(":")
price=int(pro_raw[1])
pro_raw.insert(1,price)
pro_raw.pop()
product_list.append(pro_raw)
#read balance file
balance_file=open("balance.txt","r")
bal_read=balance_file.readlines()
balance_file.close()
#write balance file
def write_balance (balance):
balance_file=open("balance.txt","w")
balance_file.write("{}".format(balance))
balance_file.close()
exit("Your shopping list is {0},your salary is {1}.".format(shopping_list,salary))
#if balance exists
if bal_read:
salary=bal_read[0]
else:
salary=input("Enter your salary:")
if salary.isdigit():
salary=int(salary)
while True:
for index,item in enumerate(product_list):
print(index+1,item)
user_choice=input("Choice a product code:")
if user_choice.isdigit():
user_choice = int(user_choice)
if user_choice <= len(product_list) and user_choice > 0:
user_choice -= 1
if product_list[user_choice][1] <= salary:
shopping_list.append(product_list[user_choice][0])
salary -= product_list[user_choice][1]
print("Added {0} to your shopping_list!Your salary is {1}\n".format(product_list[user_choice][0],salary))
else:
print("Sorry your salary is not enought!\n")
else:
print("Sorry,product code isn's exist!\n")
elif user_choice == "q":
write_balance(salary)
else:
print("Your enter invalid!\n")
else:
if salary == "q":
write_balance(salary)
else:
print("Sorry,your enter invalid!")
关于用户接口的部分到现在为止就算完成了，接下里是商家接口的。
商家接口
流程图示意
manage_product.png
流程确定好了以后，我们来想想怎么写文件比较好，之前我们的商品文件是用这种形式写的：
#cat product.txt
iphone:5800
mac pro:12000
bike:800
book:55
coffee:31
写入文件的话，需要写成
for i in list:
f.write("{0}:{1}".format(i[0],i[1]))
先试一下。复制这段代码，实验成功之后，我们再来写其他的部分。
def函数
可以多用用def函数，因为看流程图有很多动作是可以复用的。
#-*- coding:utf-8 -*-
#owner:houyizhong
#version:1.0
product_list=[]
#read product file
product_file=open("product.txt","r")
pro_read=product_file.readlines()
product_file.close()
#read the product and price
for i in pro_read:
i=i.strip()
pro_raw=i.split(":")
product_list.append(pro_raw)
def write_product ():
f=open("product.txt","w")
for i in product_list:
f.write("{0}:{1}\n".format(i[0],i[1]))
f.close()
exit()
def add_pro():
addproduct=input("Enter add product:")
addprice=input("Enter product price:")
add_list=[addproduct,addprice]
product_list.append(add_list)
print ("Your list is {}\n".format(product_list))
def w_pro():
changepro=input("Choice a product code:")
changepro = int(changepro) -1
changeprice=input("Enter product price:")
product_list[changepro][1]=changeprice
print ("Your list is {}\n".format(product_list))
def loop(enter_choice):
while True:
if enter_choice == "q":
exit()
elif enter_choice == "add":
add_pro()
pass
elif enter_choice == "w":
w_pro()
pass
elif enter_choice == "wq":
write_product()
else:
print("Sorry,your enter is invalid!\n")
for index,item in enumerate(product_list):
print (index+1,item)
print("\nEnter 'add':Added product\nEnter 'w':Change the product price\nEnter 'q':Out\nEnter 'wq':Save and exit\n")
enter_choice=input("Enter your choice:")
while True:
for index,item in enumerate(product_list):
print (index+1,item)
print("\nEnter 'add':Added product\nEnter 'w':Change the product price\nEnter 'q':Out\n")
action=input("Enter your choice:")
if action == "q":
exit()
elif action == "add":
loop(action)
pass
elif action == "w":
loop(action)
pass
else:
print("Sorry,your enter is invalid!\n")
接下来跟之前一样，需要对用户输入的choice判断边界，以及是不是数据类型，最好我们给添加一个后退选项，对用户友好些。
完成后的代码如下：
#-*- coding:utf-8 -*-
#owner:houyizhong
#version:2.0
product_list=[]
#read product file
product_file=open("product.txt","r")
pro_read=product_file.readlines()
product_file.close()
#read the product and price
for i in pro_read:
i=i.strip()
pro_raw=i.split(":")
product_list.append(pro_raw)
def write_product ():
f=open("product.txt","w")
for i in product_list:
f.write("{0}:{1}\n".format(i[0],i[1]))
f.close()
exit()
def add_pro():
addproduct=raw_input("Enter add product('b' is back):")
if addproduct == "b":
pass
else:
addprice=raw_input("Enter product price('b' is back):")
if addprice == "b":
pass
else:
add_list=[addproduct,addprice]
product_list.append(add_list)
print ("Your list is {}\n".format(product_list))
def w_pro():
while True:
changepro=raw_input("Choice a product code('b' is back):")
if changepro.isdigit():
changepro = int(changepro) -1
if not 0 <= changepro < len(product_list):
print("Sorry,your enter is not exist!\n")
else:
changeprice=raw_input("Enter product price('b' is back):")
if changeprice == "b":
pass
else:
product_list[changepro][1]=changeprice
print ("Your list is {}\n".format(product_list))
break
elif changepro == "b":
break
else:
print("Please enter a digit!\n")
def loop(enter_choice):
while True:
if enter_choice == "q":
exit()
elif enter_choice == "add":
add_pro()
pass
elif enter_choice == "w":
w_pro()
pass
elif enter_choice == "wq":
write_product()
else:
print("Sorry,your enter is invalid!\n")
for index,item in enumerate(product_list):
print (index+1,item)
print("\nEnter 'add':Added product\nEnter 'w':Change the product price\nEnter 'q':Out\nEnter 'wq':Save and exit\n")
enter_choice=raw_input("Enter your choice:")
while True:
for index,item in enumerate(product_list):
print (index+1,item)
print("\nEnter 'add':Added product\nEnter 'w':Change the product price\nEnter 'q':Out\n")
action=raw_input("Enter your choice:")
if action == "q":
exit()
elif action == "add":
loop(action)
pass
elif action == "w":
loop(action)
pass
else:
print("Sorry,your enter is invalid!\n")
到目前为止，我们已经完成了用户接口和商家接口的操作。
后续改进的意见
后续改进意见：
文件中的几个def函数 可以拿出来单独放在文件中，用import引用进来，这样方便查阅。
