Python: Nested for-loop goes through lines only once

Question

I just got started with Python this week and I wanted to put something together in order to solve a real-world problem.

Basically I am opening to files that contain URLs.

I want Python to go through each line of the file chosen for TOPICS and extract a certain part of a string, which is working fine.

While in the same loop, I want Python to go through each line of the file chosen for PAGES and check if a line contains the part of the string that was extracted beforehand. Once it does, I want Python to generate a certain output, which also works fine.

The only problem is that Python seems to run through the whole loop only once. So I am getting the correct output exactly one time and then the code ends.

This is the code I have written:

fi_topics = input('Enter TOPICS: ')
fi_pages = input('Enter PAGES: ')
h_topics = open(fi_topics)
h_pages = open(fi_pages)

for la in h_topics:
    la = la.strip()
    spos = la.find('topic/')
    topic = la[spos+6:]
    for lb in h_pages:
        lb = lb.strip()
        if topic not in lb:
            continue
        print( lb , 'https://www.exampleurl.com/t/'+topic )

Any hint on what could be the problem is highly appreciated!