Exporting List to CSV using Python

Question

I am a newbie to python and here is what I am trying to achieve. I am trying to export a python created list as a csv file but it does not seem to work.

What I am expecting to see:

Name    Address    ID
A         AA       01
B         BB       05
..       ....     ....

But this is what my output looks like unfortunately:

Name    Address    ID
['A', 'AA', '01']
['B', 'BB', '05']

In other words it is clubbing all the elements of a row in the list into the first column of the output CSV file while the header elements are in their respective columns. I am hoping to populate the entries under their respective headers in the output file. I have not encountered this problem if I am reading from a csv file and writing to one.

Here's what my code looks like:

import csv
fOpen1=open('C:\master.csv')
fOpen2=open('C:\test.csv')

masterFile=csv.reader(fOpen1)
testFile=csv.reader(fOpen2)   

outputFile=open('C:\Output.csv', 'wb')
CSVWriter=csv.writer(outputFile)

masterList=list()
testList=list()
header=testFile.next()
CSVWriter.writerow(header)

for row1 in masterFile:
    if row1[0] not in masterList:
        masterList.append(row1[0])

for row2 in testFile:
    if row2[0] not in masterList:
        testList.append(row2)

CSVWriter.writerows(zip(testList))

Where do you think I am going wrong with my code? Any help and advice would be greatly appreciated.

Anand S Kumar · Accepted Answer · 2015-08-13 07:16:04Z

1

The issue is that you are doing -

CSVWriter.writerows(zip(testList))

This causes each element in the list passed to writerows() to be a tuple with a single element, which is the list (which you see outputed to the csv). Example -

>>> l = [[1,2,3,4],[4,5,6,7],[5,5,5,5]]
>>> list(zip(l))
[([1, 2, 3, 4],), ([4, 5, 6, 7],), ([5, 5, 5, 5],)]

If you directly want to write the rows in testList, you should do -

CSVWriter.writerows(testList)

If you want to transpose the testList, so that rows become columns and columns become rows, you should unpack when sending into zip() -

CSVWriter.writerows(zip(*testList))

answered Aug 13, 2015 at 7:16

Anand S Kumar

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3 Comments

VGu Over a year ago

I was initially using the write command without zip and it wasn't working because it was transposing the rows into columns. So I started using zip. Now I removed the zip from the code and it is working perfectly fine. I feel quite stupid now. I wonder what wrong I was doing. Thank you for your quick response. It is much appreciated.

Anand S Kumar Over a year ago

You will need to show the exact code that does not work if you want to know what went wrong, maybe you were transposing the rows/columns in some other place causing the issue.

VGu Over a year ago

I have absolutely no idea now as I was continually saving the script as I was making changes. But transposing is still not clear to me. I will worry about transposing at a later stage. Thanks.

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