Readind from a CSV file and writing to a new CSV file in python

Question

Explanation: I need to take parameters from file1 and need to use in some function and then i need to take results from that function then need to write these test_name and results to a new csv i.e file2. while iam doing with below example iam getting some errors.

Readind from a CSV file1 and writing to a new CSV file2 using python

with open(inputs.csv, 'rb') as file1:  #Need to read params from this file
    data = list(csv.reader(file1))
with open('output.csv', 'wb') as file2: #Need to write results to this file
    writer = csv.writer(file2)
for row in data:
    api = row[0]
    test_name =row[1]
    out = funtion_call(api, test_name)
    writer.writerow([test_name, out])
file1.close()
file2.close()

Output:

 writer.writerow([test_name, out])
ValueError: I/O operation on closed file

Please paste the exact error message and traceback in your question, "some errors" is not a very useful information! — Thierry Lathuille
– Thierry Lathuille, Commented Jun 23, 2017 at 9:50
Installing pandas just for the sake of reading a csv file is overkill... — cs95
– cs95, Commented Jun 23, 2017 at 9:55
with open(inputs.csv, 'rb') as file1: Maybe this should be: with open('inputs.csv', 'r') as file1:. Also why 'rb' and 'wb'? You are reading a glorified text file. Not a bytes files. — selten98
– selten98, Commented Jun 23, 2017 at 10:00
hi @selten98, when iam using a single file only for read from csv i.e file1 its worked fine with 'rb'. any way i tried with your suggession as well but same error — Ravi Teja
– Ravi Teja, Commented Jun 23, 2017 at 10:05

Nick H · Accepted Answer · 2017-06-23 10:03:21Z

1

If you are using the with statment, your operations need to be within that block, with handles the opening and closing for you.

with open(inputs.csv, 'rb') as file1:  
    data = list(csv.reader(file1))
    with open('output.csv', 'wb') as file2: 
        writer = csv.writer(file2)
        for row in data:
        api = row[0]
        test_name =row[1]
        out = funtion_call(api, test_name)
        writer.writerow([test_name, out])

Without all your code, it is impossible to test this, but hopefully you get the idea. This link might help too: http://effbot.org/zone/python-with-statement.htm

answered Jun 23, 2017 at 10:03

Nick H

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2 Comments

hiro protagonist Over a year ago

true, but with open(inputs.csv, 'rb') as file1, open('output.csv', 'wb') as file2 seems much more readable - especially because there is one level of indentation fewer...

Nick H Over a year ago

@hiroprotagonist, I agree, that would be a more readable solution and would work better if there are a lot of operations on the two files.

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