Why does CSV file contain a blank line in between each data line when outputting with Dictwriter in Python

I am using DictWriter to output data in a dictionary to a csv file. Why does the CSV file have a blank line in between each data line? It's not a huge deal, but my dataset is big and doesn't fit into one csv file because it has too many lines since the "double-spacing" doubles the number of lines in the file.

My code for writing to the dictionary is:

headers=['id', 'year', 'activity', 'lineitem', 'datum']
output = csv.DictWriter(open('file3.csv','w'), delimiter=',', fieldnames=headers)
output.writerow(dict((fn,fn) for fn in headers))
for row in rows:
    output.writerow(row)

By default, the classes in the csv module use Windows-style line terminators (\r\n) rather than Unix-style (\n). Could this be what’s causing the apparent double line breaks?

If so, in python 2 you can override it in the DictWriter constructor:

output = csv.DictWriter(open('file3.csv','w'), delimiter=',', lineterminator='\n', fieldnames=headers)

From csv writer documentation:

> If csvfile is a file object, it should be opened with newline=''

In other words, when opening the file you pass newline='' as a parameter.
You can also use a with statement to close the file when you're done writing to it.
Tested example below:

from __future__ import with_statement # not necessary in newer versions
import csv
headers=['id', 'year', 'activity', 'lineitem', 'datum']
with open('file3.csv','w', newline='') as fou:
    output = csv.DictWriter(fou,delimiter=',',fieldnames=headers)
    output.writerow(dict((fn,fn) for fn in headers))
    output.writerows(rows)

Changing the 'w' (write) in this line:

output = csv.DictWriter(open('file3.csv','w'), delimiter=',', fieldnames=headers)

To 'wb' (write binary) fixed this problem for me:

output = csv.DictWriter(open('file3.csv','wb'), delimiter=',', fieldnames=headers)

Python v2.75: Open()

Credit to @dandrejvv for the solution in the comment on the original post above.

I just tested your snippet, and their is no double spacing line here. The end-of-line are \r\n, so what i would check in your case is:

1. your editor is reading correctly DOS file
2. no \n exist in values of your rows dict.

(Note that even by putting a value with \n, DictWriter automaticly quote the value.)