2

I tried to write output file as a CSV file but getting either an error or not the expected result. I am using Python 3.5.2 and 2.7 also.

Getting error in Python 3.5:

wr.writerow(var)
TypeError: a bytes-like object is required, not 'str'

and

In Python 2.7, I am getting all column result in one column.

Expected Result:
An output file same format as the input file.

Code:

import csv

f1 = open("input_1.csv", "r") 

resultFile = open("out.csv", "wb")
wr = csv.writer(resultFile, quotechar=',') 

def sort_duplicates(f1):
  for i in range(0, len(f1)):
      f1.insert(f1.index(f1[i])+1, f1[i])
      f1.pop(i+1)

for var in f1:
      #print (var)
      wr.writerow([var])

If I am using resultFile = open("out.csv", "w"), I get one row extra in the output file.

If I am using above code, getting one row and column extra.

Improve this question
2
  • You're opening the out file in binary mode. Just remove the b from the open("out.csv", "wb"). Commented Sep 12, 2016 at 10:03
  • @Sevanteri: I tried but getting one row is extra in result file Commented Sep 12, 2016 at 10:33

4 Answers 4

Reset to default
3

On Python 3, csv requires that you open the file in text mode, not binary mode. Drop the b from your file mode. You should really use newline='' too:

resultFile = open("out.csv", "w", newline='')

Better still, use the file object as a context manager to ensure it is closed automatically:

with open("input_1.csv", "r") as f1, \
     open("out.csv", "w", newline='') as resultFile:
    wr = csv.writer(resultFile, dialect='excel')
    for var in f1:
        wr.writerow([var.rstrip('\n')])

I've also stripped the lines from f1 (just to remove the newline) and put the line in a list; csv.writer.writerow wants a sequence with columns, not a single string.

Quoting the csv.writer() documentation:

If csvfile is a file object, it should be opened with newline='' [1]. [...] All other non-string data are stringified with str() before being written.

[1] If newline='' is not specified, newlines embedded inside quoted fields will not be interpreted correctly, and on platforms that use \r\n linendings on write an extra \r will be added. It should always be safe to specify newline='', since the csv module does its own (universal) newline handling.

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

5 Comments

Typically newline is required on windows or you have blank lines inserted after each lines because of the added CR chars
@Jean-FrançoisFabre: and for any other platform where \n is not the default newline character (as the \n character is going to be replaced on any of those).
@Martijn Pieters: I used newline but getting each letter is separate column
@krish: updated; you can't pass in a single string, as that'll be seen as a row with columns (each letter a separate column). I've put it in a list here.
@Martijn Pieters: thanks, now getting expected result :)
2

Others have answered that you should open the output file in text mode when using Python 3, i.e.

with open('out.csv', 'w', newline='') as resultFile:
    ...

But you also need to parse the incoming CSV data. As it is your code reads each line of the input CSV file as a single string. Then, without splitting that line into its constituent fields, it passes the string to the CSV writer. As a result, the csv.writer will treat the string as a sequence and output each character , including any terminating new line character, as a separate field. For example, if your input CSV file contains:

1,2,3,4

Your output file would be written like this:

1,",",2,",",3,",",4,"
"

You should change the for loop to this:

for row in csv.reader(f1):
    # process the row
    wr.writerow(row)

Now the input CSV file will be parsed into fields and row will contain a list of strings - one for each field. For the previous example, row would be:

for row in csv.reader(f1):
    print(row)

['1', '2', '3', '4']

And when that list is passed to the csv.writer the output to the file will be:

1,2,3,4

Putting all of that together you get this code:

import csv

with open('input_1.csv') as f1, open('out.csv', 'w', newline='') as resultFile:
    wr = csv.writer(resultFile, dialect='excel')
    for row in csv.reader(f1):
        wr.writerow(row)
Improve this answer

1 Comment

Hi All, Now I getting expected result. Thank you all :)
0

open file without b mode

b mode open your file as binary

you can open file as w

open_file = open("filename.csv", "w")
Improve this answer

Comments

0

You are opening the input file in normal read mode but the output file is opened in binary mode, correct way

resultFile = open("out.csv", "w")

As shown above if you replace "wb" with "w" it will work.

Improve this answer

1 Comment

While opening without b, I getting one row blank in result file.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.