如何在Python

Question

我正在尝试用Python编写程序进行评估，我必须更新商店的库存文件。

My instructions

到目前为止我的代码：

#open a file in read mode
file = open("data.txt","r")
#read each line of data to a vairble
FileData = file.readlines()
#close the file
file.close()

total = 0 #create the vairble total
AnotherItem = "y" # create
while AnotherItem == "y" or AnotherItem  == "Y" or  AnotherItem ==  "yes" or  AnotherItem ==  "Yes" or  AnotherItem ==  "YES":
        print("please enter the barcode")
        UsersItem=input()
        for line in  FileData:
                #split the line in to first and second section
                barcode = line.split(":")[0]
                item = line.split(":")[1]
                price = line.split(":")[2]
                stock = line.split(":")[3]

                if barcode==UsersItem:
                    file = open("data.txt","r")
                    #read each line of data to a vairble
                    FileData = file.readlines()
                    #close the file
                    file.close()
                    print(item +"       £" + str(float(price)/100) + "      Stock: " + str(stock))
                    print("how many do you want to buy")
                    HowMany= input()
                    total+=float(price) * float( HowMany)
                    file = open("data.txt","a")
                    StockLevel=float(stock)
                    file.write(item + ":" + price + ":" +str(float((StockLevel-float(HowMany)))))
                    file.close()
                    print("Do you want to buy another item? [Yes/No]")
                    AnotherItem = input()
        if AnotherItem == "n" or "N" or "no" or "No" or "NO":
                print("total price: £"+ str(total/100))

当我尝试更新我的库存文件时，它会写入数据文件的末尾，而不是我想要的那一行。

Answer 1

file = open("data.txt", "a")

以附加模式打开文件，意味着写入文件末尾而不覆盖数据（添加数据，不更改）。

使用

file = open("data.txt", "w")

相反，要刷新文件内容并覆盖它们。

如果您有一些行，并且您只想按如下方式更改最后一行：

data = open("data.txt").read().split("\n")

获取文件行数组。

data[-1] = new_line_contents

将最后一行更改为新内容。

open("data.txt", "w").write("\n".join(data))

回写并刷新新数据（将数据中的元素与新行相连接）