Python: Writing to csv-file

Question

I am trying to read a csv-style file and create another one. Here is the (simplified) code.

import os
import csv
import sys

fn = 'C:\mydird\Temp\xyz'
ext = '.txt'
infn = fn+ext
outfn = fn+'o'+ext


infile = open(infn, newline='')
outfile = open(outfn, 'w', newline='')

try:
    reader = csv.reader(infile, delimiter=',', quotechar='"')  # creates the reader object
    writer = csv.writer(outfile, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)

    for row in reader:   # iterates the rows of the file in orders
        if reader.line_num == 1 :
            print("Header")
            writer.writerow(['Date',
                'XY'])                      # ####### Does not work
        else:
#            Do something
            print(row[0],
                row[3])                     # ####### Works
            writer.writerow([row[0],
                row[3]])                    # ####### Does not work
finally:
    infile.close()      # closing

sys.exit(0))

Neither of the writerow statements generate output.

The file is created, but is empty.

The print statement creates 'expected' ouput.

I have also tried already csv.DictWriter with no success either.

I have looked at the various simlar questions, but can't see any difference.

I am using Py 3.3.3 on a win 7 machine.

EDIT:

the writer got lost be code simplification

you do not define writer or close the outfile

Tadhg McDonald-Jensen
– Tadhg McDonald-Jensen

2016-06-24 18:31:06 +00:00
Commented Jun 24, 2016 at 18:31 — Tadhg McDonald-Jensen
– Tadhg McDonald-Jensen, Commented Jun 24, 2016 at 18:31

dr jimbob · Accepted Answer · 2016-06-24 18:34:38Z

4

Your code doesn't define a writer.

Add writer = csv.writer(outfile) and then close the outfile and it should work. Using the with idiom makes the code cleaner.

import csv

fn = 'C:\mydird\Temp\xyz'
ext = '.txt'
infn = fn+ext
outfn = fn+'o'+ext

with open(infn) as rf, open(outfn, 'w') as wf:
    reader = csv.reader(rf, delimiter=',', quotechar='"')
    writer = csv.writer(wf)
    for row in reader:   # iterates the rows of the file in orders
        if reader.line_num == 1 :
           print("Header")
           writer.writerow(['Date', 'XY'])
        else:
           # do something
            print(row[0], row[3])
            writer.writerow([row[0], row[3]])

edited Jun 24, 2016 at 18:34

answered Jun 24, 2016 at 18:29

dr jimbob

17.8k7 gold badges63 silver badges84 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kurt Ludikovsky Over a year ago

It's been the close.

Collectives™ on Stack Overflow

Python: Writing to csv-file

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related