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Actually i am trying to export a csv file with some data and below is my code

import csv
from cStringIO import StringIO
import web


def download(list__of_records):
    csv_file = StringIO()
    csv_writer = csv.writer(csv_file)
    csv_writer.writerow(['Name', 'Link'])
    for i in list_of_records :
         csv_writer.writerow([i[0],i[1]])
    web.header('Content-Type','text/csv')       
    web.header('Content-disposition', 'attachment; filename=%s.csv'%file_name) 
    return csv_file.getvalue()

list_of_records_1 = [('name',"fedrik"),('age','73'),('city','portland')]
list_of_records_2 = [('name',"wow"),('age','466'),('city','asdsa')]

download(list_of_records_1)

Actually i will use the above code in some web page that downloads a csv with the list_of_records data.

In the above code i am using web which is nothing but web.py framework i ma using to instruct browser to download a csv ifle

suppose i called the function download(list_of_records_1) , then a csv file is downloaded with data in it as below

Name    fedrik
age         73
city        portland

suppose i call the same function with download(list_of_records_2) , the output saving in to the csv is as below

Name    fedrik
age         73
city        portland
Name    wow
age         466
city        asd

That is if the data already matching in csv then its overwriting and if new data is encountered then the csv file is creating with previous data as well as present list_of_records_2 data.

So in the above code after storing the results in the buffer string StringIO() and saving in to csv file, we should truncate/delete the buffer string data, so that when we call the same function with other list of results the previous data will not be write in to csv file of the current one

Can anyone please let me know how to truncate the buffer string StringIO() in the above code ?

dwitvliet
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Shiva Krishna Bavandla
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  • you know StringIO has a truncate() method, like for normal files? – isedev Feb 22 '13 at 11:28
  • yup but i tried and its not truncating the buffer string so approached SO, can u please refer here http://stackoverflow.com/questions/15019549/downloading-exporting-a-csv-file-when-clicked-on-a-button-in-web-py-python This was my actual problem – Shiva Krishna Bavandla Feb 22 '13 at 11:30
  • @MartijnPieters -- don't agree: "s = StringIO.StringIO(); s.write('hello world\n'); s.truncate(0); s.seek(0); s.read()" -> returns empty string. – isedev Feb 22 '13 at 11:39
  • I may as well delete my answer, because your diagnosis of what is going wrong is not correct. You create a new `StringIO()` instance every time in `download()` so I think you are doing something else wrong here. – Martijn Pieters Feb 22 '13 at 11:39
  • @isedev: Ah, I forgot there is an argument to `.truncate()` :-) – Martijn Pieters Feb 22 '13 at 11:40
  • To make it absolutely clear: Creating a *new* `StringIO` object each time means it can *never* contain data from a previous CSV file. – Martijn Pieters Feb 22 '13 at 12:00
  • Actually in my code i declared a shared variable web.some_vriable = [], which i am updating in every class, here i am looping through this list and saving the results to csv, probably this is the result for this, after completion of generating csv i should empty this list so that it will contains the data only from the next url in my scenario:) presently trying to check this out – Shiva Krishna Bavandla Feb 22 '13 at 12:18

0 Answers0