file_one = open('file1.txt', 'r')
file_two = open('file2.txt', 'r')

content = file_one.readlines()
content_2 = file_two.readlines()

non_match = []

for line in content:
    for other_line in content_2:
        if line != other_line and line not in non_match:
            non_match.append(line)

print(('n').join(non_match))

file_one.close()
file_two.close()

(xenial)vash@localhost:~$ python3.7 search.py
neighbor 192.168.3.1 remote-as 200

neighbor 192.168.4.1 remote-as 300

neighbor 192.168.15.1 remote-as 400

neighbor 192.168.16.1 remote-as 500

neighbor 20.249.208.165 remote-as 200

neighbor 80.249.208.165 remote-as 100

neighbor 192.168.5.1 remote-as 400