Just run the code by using python3 extract-user-id.py or py extract-user-id.py in the intended folder with the files you want to extract.
I am not good at python 2 so I am unsure if it works on python 2.
The user IDs will be saved in the same directory with 2 files (one with duplicates, and the other without). "user_id_new.txt" and "user_id_new_1.txt"