for loop and nested for loop [closed]

Answer 1

Creating a dictionary out of the lines in second file would be a faster solution and it will get rid of the duplicates too:

from collections import defaultdict

second_file = open('second.txt')
second_file_dict = defaultdict(int)
first_file_dict = defaultdict(int)

for line in second_file:
    second_file_dict[line.strip()] += 1
second_file.close()

first_file = open('first.txt')
for line in first_file:
    if line in second_file_dict and not in first_file_dict:
        print line
    first_file_dict[line.strip()] += 1        
first_file.close()