Writing to a mac csv not working using python file writter

I have a python code where it compares two files and returns the common lines and writes them to a result file. I am using a MAC machine.

script.py

with open('temp1.csv', 'r') as file1:
    with open('serialnumbers.txt', 'r') as file2:
        same = set(file1).intersection(file2)
        print same

with open('results.csv', 'w') as file_out:
    for line in same:
        file_out.write(line)
        print line

temp1.csv

M11435TDS144
M11543TH4292
SN005
M11509TD9937
M11543TH4258
SN005
SN006
SN007

serialnumbers.txt

G1A114042400571
M11251TH1230
M11543TH4258
M11435TDS144
M11543TH4292
M11509TD9937

The output of the above script on mac is

set([])

If I run the same script on windows it is working fine. I found out that this is a csv problem on mac. How can I resolve this issue?