More efficient way to convert a nested list to .csv in python

Question

I've a nested list like Python_List below and I want to make a .csv like below:

    Python_List|->  .csv
    [['2','4'],|     2,4   
     ['6','7'],|     6,7
     ['5','9'],|     5,9
     ['4','7']]|     4,7

So far I'm using this code:

Python_List=[['2','4'],  ['6','7'], ['5','9'], ['4','7']]
with open('test.csv','w') as f:
    for i in range(0,len(Python_List)):
        f.write('%s,%s\n' %(Python_List[i][0],Python_List[i][1]))

Are there any alternatives more efficient?

A remark on your for-loop: You do not need to loop through indexes. Instead loop over the elements themselves for l in Python_List:, then the next line reduces to f.write('%s,%s\n' % tuple(l)). Anyway you should use csv.writer. — user3072164
– user3072164, Commented Jan 3, 2014 at 10:36
@Nabla thanks this is a very useful trick feel free to post an answer is a nice way to do what I want! — G M
– G M, Commented Jan 3, 2014 at 10:45

Robert Christie · Accepted Answer · 2014-01-03 10:30:52Z

4

Consider using the writer method of the csv module.

It may not be more efficient but it will be easier to understand.

For Example

import csv
with open('test.csv', 'w') as csvfile:
    csvwriter = csv.writer(csvfile, delimiter=',')
    csvwriter.writerows(Python_List)

answered Jan 3, 2014 at 10:30

Robert Christie

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Burhan Khalid · Accepted Answer · 2014-01-03 10:33:39Z

2

>>> i = [['2','4'],  ['6','7'], ['5','9'], ['4','7']]
>>> with open('test.csv','w') as f:
...    writer = csv.writer(f)
...    writer.writerows(i)
... 
>>> quit()
$ cat test.csv
2,4
6,7
5,9
4,7

answered Jan 3, 2014 at 10:33

Burhan Khalid

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thefourtheye · Accepted Answer · 2014-01-03 10:32:51Z

1

You can csv module and its writer method, like this

pyList = [['2','4'],  ['6','7'], ['5','9'], ['4','7']]
import csv
with open('Output.txt', 'wb') as csvfile:
    csvwriter = csv.writer(csvfile, delimiter=',')
    map(csvwriter.writerow, pyList)

answered Jan 3, 2014 at 10:32

thefourtheye

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