I'm trying to obtain the difference between two csv files A.csv and B.csv in order to obtain new rows added in the second file. A.csv has the following data.

acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    Redundant/RSK

B.csv has the following data.

acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    Redundant/RSK
acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    DT/89

To write the new rows added into an output file I'm using the following script.

input_file1 = "A.csv"
input_file2 = "B.csv"
output_path = "out.csv"with open(input_file1, 'r') as t1:fileone = set(t1)
with open(input_file2, 'r') as t2, open(output_path, 'w') as outFile:for line in t2:if line not in fileone:outFile.write(line)

Expected output is :

acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    DT/89 

Output obtained through the above script is :

acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    Redundant/RSK
acct    ABC     88888888    99999999    ABC-GHD 4/1/18  4   1   2018    DT/89

I'm not sure where I'm making a mistake, tried debugging it but with no progress.

You need to be careful with trailing newlines. As such it is safer to remove the newlines before comparing and then add them back when writing:

input_file1 = "A.csv"
input_file2 = "B.csv"
output_path = "out.csv"with open(input_file1, 'r') as t1:fileone = set(t1.read().splitlines())with open(input_file2, 'r') as t2, open(output_path, 'w') as outFile:for line in t2:line = line.strip()if line not in fileone:outFile.write(line + '\n')