如何使用Python向CSV文件中添加新列？ [英] How to add a new column to a CSV file using Python?

问题描述

我有几个 CSV 文件，如下所示：

I have several CSV files that look like this:

Input    
Name        Code    
blackberry  1   
wineberry   2   
rasberry    1   
blueberry   1   
mulberry    2

我想为所有CSV文件添加一个新列，如下所示： / p>

I would like to add a new column to all CSV files so that it would look like this:

Output   
Name        Code    Berry               
blackberry  1   blackberry  
wineberry   2   wineberry           
rasberry    1   rasberry        
blueberry   1   blueberry       
mulberry    2   mulberry     

远的是这：

import csv
with open(input.csv,'r') as csvinput:
    with open(output.csv, 'w') as csvoutput:
        writer = csv.writer(csvoutput)
        for row in csv.reader(csvinput):
            writer.writerow(row+['Berry'])

（Python 3.2）

(Python 3.2)

但是在输出中，脚本跳过每一行，新列只有Berry。

But in the output, the script skips every line and the new column has only Berry in it:

Output   
Name        Code    Berry               
blackberry  1   Berry   

wineberry   2   Berry   

rasberry    1   Berry   

blueberry   1   Berry       

mulberry    2   Berry     

推荐答案

你想要做什么：

>>> v = open('C:/test/test.csv')
>>> r = csv.reader(v)
>>> row0 = r.next()
>>> row0.append('berry')
>>> print row0
['Name', 'Code', 'berry']
>>> for item in r:
...     item.append(item[0])
...     print item
...     
['blackberry', '1', 'blackberry']
['wineberry', '2', 'wineberry']
['rasberry', '1', 'rasberry']
['blueberry', '1', 'blueberry']
['mulberry', '2', 'mulberry']
>>> 

编辑，注意在py3k你必须使用 next（r）

Edit, note in py3k you must use next(r)

感谢您接受答案。这里有一个奖励（你的工作脚本）：

Thanks for accepting the answer. Here you have a bonus (your working script):

import csv

with open('C:/test/test.csv','r') as csvinput:
    with open('C:/test/output.csv', 'w') as csvoutput:
        writer = csv.writer(csvoutput, lineterminator='\n')
        reader = csv.reader(csvinput)

        all = []
        row = next(reader)
        row.append('Berry')
        all.append(row)

        for row in reader:
            row.append(row[0])
            all.append(row)

        writer.writerows(all)

p>

Please note

1. 中的 lineterminator 参数csv.writer 。默认情况下，
   设置为'\r\\\
'，这就是为什么你有双倍间距。


2. 使用列表来附加所有行，并在
   中用 writerows 一次性写入。如果你的文件是非常，非常大这
   可能不是一个好主意（RAM），但对于正常文件，我认为它是
   更快，因为有更少的I / O。



3. 如这篇文章的注释所示，请注意，不是
   嵌套两个和语句，你可以在同一个行：

1. the lineterminator parameter in csv.writer. By default it is set to '\r\n' and this is why you have double spacing.
2. the use of a list to append all the lines and to write them in one shot with writerows. If your file is very, very big this probably is not a good idea (RAM) but for normal files I think it is faster because there is less I/O.

3. As indicated in the comments to this post, note that instead of nesting the two with statements, you can do it in the same line:

打开（'C：/test/test.csv'，'r'）as csvinput，open（'C：/test/output.csv' ，'w'）as csvoutput：

with open('C:/test/test.csv','r') as csvinput, open('C:/test/output.csv', 'w') as csvoutput:

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