How to multiply lines from two different text files into one text file in Python?

How to multiply lines from two different text files into one text file in Python?

I would like the result sequence to be as follows

| result |
| zzzzzzbbbbbb |
| zzzzzzffffff |
| zzzzzzkkkkkk |
| aaaaaabbbbbb |
| aaaaaaffffff |
| aaaaaakkkkkk |
| nnnnnnbbbbbb |
| nnnnnnffffff |
| nnnnnnkkkkkk |

I'm tired trying to make this code or find something similar, so many thanks to anyone who helps me with the solution.

def write_files(files):
    opened_files = []
    for f in files:
        opened_files.append(open(f, "r"))

    output_file = open("result.txt", "w")
    num_lines = sum(1 for line in opened_files[0])
    opened_files[0].seek(0,0)
    for i in range(num_lines):
        line = [of.readline().rstrip() for of in opened_files]
        line = " ".join(line)
        line += "\n"
        output_file.write(line)
    for of in opened_files:
        of.close()
    output_file.close()

write_files(["1.txt", "2.txt"])

The easy way is to use itertools.product:

import itertools

def write(files):
    data = [ open(f).read().splitlines() for f in files]
    return [''.join(t) for t in itertools.product(*data)]

print('\n'.join(write(['f1.txt','f2.txt'])))

Output:

zzzzzzbbbbbb
zzzzzzffffff
zzzzzzkkkkkk
aaaaaabbbbbb
aaaaaaffffff
aaaaaakkkkkk
nnnnnnbbbbbb
nnnnnnffffff
nnnnnnkkkkkk

Note, however, that the list grows really big very quickly.