如何在csv文件的每一行写一个值？

Question

我使用循环计算csv文件的每一行的值，并希望将此值写为每行中的新列。

我打开文件：

with open('hello.csv', 'r', encoding="latin-1") as csvfile:
    readCSV = csv.reader(csvfile, delimiter=',')
    list1 = list(readCSV)

然后循环遍历行并计算新值：

for j in list1:
    dt=j[1]
    dt2=dt+1

如何在每行“j”中将dt2写为现有csv文件“hello.csv”中的新列？

复制评论：

这只是一个简单的例子。我已将数据时间对象转换为正确的时区：

dtstr=j[1] #string 
hours, minutes = [int(t) for t in tstr.split(':')] 
dt = datetime.strptime(dtstr, '%Y-%m-%d %H:%M:%S') + 
              timedelta(hours=hours+4, minutes=minutes)

Answer 1

使用python csv模块创建一个新列并在outfile中写入行，并使用new_column_value添加新列表。

with open('hello.csv', 'r', encoding="latin-1") as csvfile:
    readCSV = csv.reader(csvfile, delimiter=',')
    with open('helloout.csv', 'w', encoding="latin-1") as outfile:
        outCSV = csv.writer(outfile,delimiter=',')
        for line in readCSV:
            new_column_value = func(line[j]) # Your modification function j column number
            new_line = line + [new_column_value]
            outCSV.writerow(newline)

Answer 2

 with open('hello.csv', 'r', encoding="latin-1") as csvfile:
          readCSV = csv.reader(csvfile, delimiter=',')
          list1 = list(readCSV)
          for j in list1:
              dtstr=j[1] #string
              hours, minutes = [int(t) for t in tstr.split(':')]
              dt = datetime.strptime(dtstr, '%Y-%m-%d %H:%M:%S')         +timedelta(hours=hours+4, minutes=minutes)
              with open('hello out.csv', 'w', encoding="latin-1") as outfile:
                    outCSV = csv.writer(outfile,delimiter=',')
                    newline = j + [dt]
                    outCSV.writerow(newline)

我只用一行成为一个csv文件helloout.csv，这是带有新列的文件hello.csv的最后一行。我认为它会覆盖行但我不明白为什么？