Using os.walk in Python 3.10
My code

import os

def generate_dir_report(path, report_file_path):
    print("n ---- Starting generate_dir_report ----")
 
    # open file
    f = open(report_file_path,  "w")

    for root, dirs, files in sorted(os.walk(path)):
        for file_name in sorted(files):
            # write the `root` string into the `out` file as a single line>
            # fix print(root)
            print(root)
            f.write(root + "n") 

            # write the `root` string into the `out` file as a single line>
            for file_name in sorted(files):
                # write the `file_name` string into the `out` file as a single line
                print(file_name)
                f.write(file_name + "n")

    f.close()
    print(" ---- Done ----n")

generate_dir_report('data/dir-top','dir-report.txt')

Expected results

data/dir-top
file1.txt
file2.txt
data/dir-top/dir1
file3.txt
data/dir-top/dir2
file6.txt
file7.log
data/dir-top/dir3
file4.log
data/dir-top/dir3/dir4
file5.txt

Actual result

---- Starting generate_dir_report ----
data/dir-top
file1.txt
file2.txt
data/dir-top
file1.txt
file2.txt
data/dir-top/dir1
file3.txt
data/dir-top/dir2
file6.txt
file7.log
data/dir-top/dir2
file6.txt
file7.log
data/dir-top/dir3
file4.log
data/dir-top/dir3/dir4
file5.txt
 ---- Done ----

The first expected entry (first 3 lines) seem to be duplicated 2x in my actual results. The same happens again so that the total expected lines are 12 and the total actual lines are 18.

I have duplicated the issue on Windows, and a web-based virtualization I am using; the results are consistent in both cases.