python CSV writer-格式化 [英] python CSV writer - formatting

问题描述

关于如何使用python csv模块将数据正确写回CSV文件的快速问题.目前，我正在导入文件，使用datetime模块提取一列日期并创建days_of_the_week列.然后，我想写出一个包含一个原始元素和新元素的新csv文件(或覆盖单个文件).

Quick question on how to properly write data back into a CSV file using the python csv module. Currently i'm importing a file, pulling a column of dates and making a column of days_of_the_week using the datetime module. I want to then write out a new csv file (or overright the individual one) containing one original element and the new element.

with open('new_dates.csv') as csvfile2:
    readCSV2 = csv.reader(csvfile2, delimiter=',')
    incoming = []
    for row in readCSV2:
         readin = row[0]
         time = row[1]
         year, month, day = (int(x) for x in readin.split('-'))
         ans = datetime.date(year, month, day)
         wkday = ans.strftime("%A")
         incoming.append(wkday)
         incoming.append(time)
with open('new_dates2.csv', 'w') as out_file:
    out_file.write('\n'.join(incoming))

输入文件如下:

2017-03-02,09:25
2017-03-01,06:45
2017-02-28,23:49
2017-02-28,19:34

使用此代码时，我得到的输出文件如下所示:

When using this code I end up with an output file that looks like this:

Friday
15:23
Friday
14:41
Friday
13:54
Friday
7:13 

我需要的是一个看起来像这样的输出文件:

What I need is an output file that looks like this:

Friday,15:23
Friday,14:41
Friday,13:54
Friday,7:13 

如果我将out_file.write中的定界符更改为逗号，则每列只会得到一个数据元素，就像这样:

If I change the delimiter in out_file.write to a comma I just get one element of data per column, like this:

Friday  15:23   Friday 14:41  Friday 13:54  ....

任何想法都将不胜感激.谢谢！

Any thoughts would be appreciated. Thanks!

推荐答案

似乎您希望在第0列中输入Friday并在第1列中输入时间，因此您需要将incoming更改为列表列表.这意味着append语句应如下所示:

It seems you want Friday in column 0 and the time in column 1, so you need to change your incoming to a list of lists. That means the append statement should look like this:

...
    incoming.append([wkday, time])
...

然后，最好使用csv.writer写回文件.您可以一次性编写整个incoming，而不必担心格式.

Then, it is better to use the csv.writer to write back to the file. You can write the whole incoming in one go without worrying about formatting.

with open('new_dates2.csv', 'w') as out_file:
    writer = csv.writer(out_file)
    writer.writerows(incoming)

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