数组数据在功能之外的变化

Question

我正在编写一个函数，用于获取每年购买的软件许可证&返回每个月花费的金额。所以投入。

#[company id, user id, purchase amount, date in yy-mm format, day when customer first registered]
['55463', '114769', $200, '14-5', '2/14/2013']

会回来

['55463', '114769', $17.5, '14-5', '2/14/2013']
['55463', '114769', $17.5, '14-6', '2/14/2013']
['55463', '114769', $17.5, '14-7', '2/14/2013']
['55463', '114769', $17.5, '14-8', '2/14/2013']

等等，我有一个函数，可以按需要打印出来。但是，当我试图访问函数外部的数据时，我写入的数组在上个月突然显示了多次重复。所以最后一个例子就是。

['55463', '114769', $17.5, '14-8', '2/14/2013']
['55463', '114769', $17.5, '14-8', '2/14/2013']
['55463', '114769', $17.5, '14-8', '2/14/2013']
['55463', '114769', $17.5, '14-8', '2/14/2013']

我不知道这是为了我的生命&我会非常感谢任何帮助。这是我的密码。我相信错误在for循环中的某个位置，在范围(11)中的x开始。谢谢你的帮助!

line_items = []
annualized = []
def csv_dict_reader(file_obj):
global board_info 
reader = csv.DictReader(file_obj, delimiter=',')
for line in reader:
    item = []
    item.append(line["company id"])
    item.append(line["user id"])
    item.append(line["Amount"])
    item.append(line["Transaction Date"])
    item.append(line["FIrst Transaction"])
    line_items.append(item)
if __name__ == "__main__":
with open("ChurnTest.csv") as f_obj:
    csv_dict_reader(f_obj)

def dateSplit():
for i in range(1,4192):
    line = line_items[i]
    amount = line_items[i][2]
    if len(amount) > 1 and line_items[i][1] == '114769':
        if float(amount) > 150:
                line_items[i][2] = float(amount) / 12
                #monthly_transactions.append(line_items[i])
                year = int(line[3][:2])
                month = int(line[3][4:])
                for x in range(11):
                    month = int(month)            
                    year = int(year)
                    newLine = line_items[i]
                    if month > 11:
                        year = year + 1
                        month = 1
                    else:
                        month = month + 1
                    newLine[3] = str(year) + "-" + str(month)
                    annualized.append(newLine)
                    #This prints out the data as I want it to be
                    print(annualized[len(annualized)-1])
        else:
            monthly_transactions.append(line_items[i])

dateSplit()
#This prints out the data incorrectly.
print(annualized)

Answer 1

关于错误的来源，您是正确的，它在循环for x in range(11):中。这一行：

 newLine = line_items[i]

不创建一个新对象。Python列表是可变的，所以即使您编辑了它，newLine仍然引用annualized和line_items中相同的对象。最小的解决办法是：

newLine = line_items[i][:] # or 'line[:]' - see below

这使得newLine在每个循环中都是一个单独的副本。

有关名称和参考的更多信息，您可能应该阅读这和这。

为什么分配line然后继续引用line_items[i]？而且，硬代码4192看起来真的很奇怪；您可以不做for line in line_items[1:]:吗？